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Revista de Biología Tropical, ISSN: 2215-2075 Vol. 69(Suppl. 2): S74-S93, October 2021 (Published Oct. 30, 2021)

Hydrographic variability in the Gulf of Papagayo,

Costa Rica during 2017-2019

Sergio Cambronero-Solano

1,2

; https://orcid.org/0000-0002-3429-8672

Alexandre Tisseaux-Navarro

; https://orcid.org/0000-0003-2634-2036

José Mauro Vargas-Hernández

; https://orcid.org/0000-0002-7014-7054

Juan P. Salazar-Ceciliano

; https://orcid.org/0000-0002-6951-5286

Rosario Benavides-Morera

; https://orcid.org/0000-0002-8570-8280

Isabel Quesada-Ávila

; https://orcid.org/0000-0002-3737-612X

Carlos Brenes-Rodríguez

; https://orcid.org/0000-0002-7814-7673

1. Laboratorio de Oceanografía y Manejo Costero, Universidad Nacional, Costa Rica;

sergio.cambronero.solano@una.cr, alexandre.tisseaux.navarro@una.cr, juan.salazar.ceciliano@una.cr,

isabel.quesada.avila@est.una.ac.cr

2. Servicio Regional de Información Oceanográfica, Universidad Nacional, Costa Rica; mauro@una.cr,

rosario.benavides.morera@una.cr, cbrenes.una@gmail.com

Received 30-I-2021. Corrected 19-IV-2021. Accepted 28-VI-2021.

ABSTRACT

Introduction: The Gulf of Papagayo (GP) is a site of socioeconomic importance located in the North Pacific of

Costa Rica. The ecosystem services of this site represent a benefit in local communities, and its dynamics are

influenced by a coastal upwelling system that affects fishing and commercial activity.

Objective: The objective of this study was to characterize the spatio-temporal variability of the main hydro-

graphic parameters through measurements in situ during the period 2017-2019.

Methods: Eight measurement campaigns were carried out, where a CTD probe was deployed to perform verti-

cal profiles in 23 stations distributed throughout the GP, to characterize the variations in temperature, salinity,

dissolved oxygen and chlorophyll concentration.

Results: A minimum in surface and bottom temperature associated with upwelling caused by the wind was

found in the first period of the year. The increase in salinity was associated with the decrease in temperature,

being its highest value in the first period of the year, decreasing until reaching a minimum in November. The

maximum chlorophyll concentration coincided with the lowest surface temperatures and the minimum oxygen

values were associated with the minimum bottom temperatures, both occurring during the upwelling season.

The parameter distribution was similar on dry and rainy seasons in stations located inside Bahía Culebra, likely

attributed to the bathymetry effect.

Conclusions: Bathymetry determines a south-north asymmetry for salinity and temperature. Subsurface cooling

events coincide with strong wind periods. Upwelling influences the surface and bottom hydrographic dynamic in

GP and determines the seasonal variability. The negative ENSO phase of 2018 corresponded with the strongest

upwelling period, possibly promoting the interaction of upwelled coastal waters and the Costa Rica Thermal

Dome.

Key words: upwelling; Eastern Tropical Pacific; hydrography; ENSO; Gulf of Papagayo.

Cambronero-Solano, S., Tisseaux-Navarro, A., Vargas-

Hernández, J. M., Salazar-Ceciliano, J. P., Benavides-

Morera, R., Quesada-Ávila, I., & Brenes-Rodríguez, C.

(2021). Hydrographic variability in the Gulf of Papagayo,

Costa Rica during 2017-2019. Revista de Biología

Tropical, 69(Suppl. 2), S74-S93. https://doi.org/10.15517/

rbt.v69iS2.48308

https://doi.org/10.15517/rbt.v69iS2.48308

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The Gulf of Papagayo (GP) is in a region

of high socioeconomic importance in the North

Pacific of Costa Rica, where Bahía Culebra

(BC) is the main center of tourism development

in Costa Rica and Central America (Cajiao,

2012; Fig. 1). Located from Matapalo (Punta

Gorda) up to the Santa Elena Peninsula, this

gulf is influenced by one of three local upwell-

ing ecosystems off the Pacific coast of Central

America, which are generated by wind jets from

high-pressure systems in the Gulf of Mexico

and the Caribbean passing westward through

mountain gaps in the isthmus (McCreary, Lee,

& Enfield, 1989). Wind gusts can reach up to

50 ms

-1

at 10 m from the ground (Amador et

al., 2006) and monthly average wind speed

can reach 8 ms

-1

(Gómez, García, & Álvarez,

2012). These wind jets spread offshore as far as

500 km off the Pacific coast, and have a time

scale in the order of weeks (Fiedler & Talley,

2006; Kessler, 2006).

It has been documented that funneling

northeasterly winds through passages in the

mountains produce upwelling in semi-enclosed

bodies in the Pacific coast of Costa Rica

(Brenes et al., 2003) and is the most important

source of seasonal variability in GP (Fiedler

& Lavin, 2017). Strong-wind conditions are

associated with vertical mixing and upwelling

events because of Ekman pumping (Kessler,

2006). This influences the hydrography and

composition of planktonic communities in GP,

with the consequent transmission of energy

at higher trophic levels (Ballestero, Márquez,

Salazar, & Murillo, 2012). Some of these

events induce long-lived anticyclonic eddies

with diameters between 100-450 km, which

propagate westward and equatorward into the

Eastern Tropical Pacific (ETP) (Ballestero &

Coen, 2004, Vargas 2002).

GP is in the ETP, a region off the coast

of Central America and Mexico, delimited by

Baja California to the North and Peru to the

South (Fiedler & Talley, 2006). This is one of

the most complex oceanic regimes, where a

wide variety of physical processes produce a

coupled ocean-atmosphere system. According

to McClain et al. (2012), surface meteorologi-

cal processes such as wind stress patterns, heat

fluxes and precipitation drive oceanic reactions

such as vertical mixing, Ekman divergence,

and a variety of wave modes such as Kelvin,

Fig. 1. Position of CTD casts done in the Gulf of Papagayo, Costa Rica. Arrows indicate the position of transects used

to represent cross-sections. Bathymetric data were obtained from the General Bathymetric Chart of the Oceans (GEBCO

Compilation Group, 2020).

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Rossby, Yanai and Kelvin-Helmholtz shear

instabilities (Ménesguen et al., 2019)

Two major oceanographic conditions

strongly influence the hydrographic variability

in the ETP (Fiedler & Lavin, 2017). Primar-

ily, the Costa Rica Thermal Dome (CRTD),

an upwelling region located off the coast of

Nicaraguan and Costa Rican Pacific coast

that affects the regional temperature distribu-

tion, as it represents the end of a thermocline

ridge which shoals from west to east across the

Pacific. CRTD is associated with local winds

and the Equatorial Counter Current (Hofmann,

Busalacchi, & Q’Brien, 1981), this is of par-

ticular interest for GP as thermocline doming

begins due to Ekman pumping near the coast in

February-March (Fiedler, 2002). While CRTD

is considered a mesoscale feature (McClain

et al., 2002) with seasonal variability, lower

frequency conditions such as El Niño-Southern

Oscillation (ENSO) also influence the regional

hydrography. During the positive phase of

ENSO, sea surface temperature (SST) increase

in the region, while on the negative phase

(“La Niña”), SST drops significantly (Wolter

& Timlin, 2011). In this regard, it has been

demonstrated that ENSO dominates the inter-

annual variability in GP (Alfaro et al., 2012).

In addition, the position of the intertropi-

cal convergence zone (ITCZ) also influences

the hydrography of the region, particularly in

coastal areas where river runoff can modify

local conditions.

The physical complexity of GP makes it a

unique ecological environment within the ETP,

with a variety of understudied coastal environ-

ments (Álvarez, Benavides-Morera, Brenes-

Rodríguez, & Saxon, 2018) such as mangroves,

sandy substrates, seagrass meadows, coastal

islands, and rocky and coral reefs (May-Colla-

do & Morales, 2005). The ecosystem services

provided by GP are important since some of

the most developed coral reefs in Costa Rica

can be found in GP at Islas Murciélago and

BC (Jiménez & Cortés, 2003). Additionally,

the seasonality in GP is known to influence the

presence of economically important species

such as humpback whales, dolphins, sharks,

squids, tuna and billfishes; this has made this

place of particular interest for tourism and

fisheries (Calambokidis, 2000; May-Collado,

2001; SINAC, 2008; Villalobos-Rojas, Herre-

ra-Correal, Garita-Alvarado, Clarke, & Beita-

Jiménez, 2014)

Tourism, conservation and restoration

projects have increased over the last years in

this area and have raised the need for proper

management of marine resources. To achieve

this, it is critical to understand the seasonal

variability of the local and regional hydrog-

raphy. Some of these relationships have been

described in the past (Ballestero & Coen,

2004; Brenes, Lavin, & Mascarenhas, 2008;

Vargas-Hernández, Salazar-Ceciliano, Bena-

vides-Morera, Tisseaux-Navarro, & Cambro-

nero-Solano, 2019; Wyrtki, 1966), but there

is a lack of comprehensive studies. Therefore,

the objective of this work was to describe the

hydrographic variations in the dry and rainy

seasons in GP during the 2017-2019 period.

MATERIALS AND METHODS

Study area: The GP has an approximate

area of 600 km

. Álvarez et al. (2018) indicated

that the maximum depth in this area is ~100

m. According to IMN (2008) the climatology

shows a clearly defined dry and rainy season,

with a period of low precipitation between

December and March, followed by two periods

of high precipitation (Fig. 2): from May to June

and then from August to October (Alfaro &

Cortés, 2012; Alfaro et al., 2012). These maxi-

mums are separated by a period of decreased

precipitation, normally observed in July, called

Mid-Summer Drought (also known as ‘vera-

nillo de San Juan’ or ‘canícula’) (Alfaro, 2014;

Magaña, Amador, & Medina, 1999). April and

November are transition periods between the

dry and rainy seasons (Gotlieb, Pérez-Briceño,

Hidalgo, & Alfaro, 2019; Lizano & Alfaro,

2014; Taylor & Alfaro, 2005).

Data collection and analysis: We carried

out eight measurement campaigns in the study

area (22/02/2017, 07/09/2017, 23/11/2017,

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28/02/2018, 12/09/2018, 27/11/2018,

20/03/2019 and 12/09/2019). The study area

covered 350 km

, where vertical profiles of

salinity, temperature, chlorophyll-a fluores-

cence, and dissolved oxygen concentration

were recorded at 23 sampling stations. The 23

stations were sampled on all campaigns (Fig.

1) using two CTD sondes, an SBE19-Plus

(sampling frequency: 4 Hz, SeaBird Scientific)

and EXO1 (sampling frequency: 1 Hz, YSI).

The EXO1 was used instead of the SBE-19Plus

in the first 3 three campaigns. Vertical profile

data for the analyses were obtained only from

the CTD sonde downcast. To further examine

the spatial variability, stations were grouped in

three transects, two longitudinal vertical sec-

tions across BC (T1) and off Naranjo Beach

(T2), consisting of stations 18 to 23 for T1

and stations 5 to 8 for T2. The third transect

comprised stations 23, 17, 9, 8 and 1 (T3), rep-

resenting a latitudinal perspective in a stream-

wise direction.

CTD was towed manually at a constant

speed between 0.2-0.4 m/s, filtering all data

less than 0.15 m/s. The data for conserva-

tive temperature (°C), absolute salinity (g/kg),

chlorophyll-a concentration (mg/m

), and opti-

cal dissolved oxygen (mg/L) were averaged

every 0.5 m and outliers were removed based

on modified z-scores of the data set (Cho, Oh,

Kim, & Shim, 2013; Virtanen, 2020). The hori-

zontal distribution of properties at the surface

and bottom were generated using the krigging

method on standardized grids of 200 nodes in

longitude and 250 in latitude. Oxygen data for

February 2017 was excluded from the analyses

due to technical problems with the CTD that

produced invalid figures.

“To evaluate seasonality and possible

interrelations of GP with the ENSO, we used 11

micron night-sea surface temperature (MODI-

SA_L3m_NSST_Monthly_4km vR2019.0;

GPS coordinates: 10.5791 & -86.3503;

10.7769 & -85.823) and chlorophyll-a con-

centration (MODISA_L3m_CHL v2018; GPS

coordinates: 10.4792 & -86.8125; 10.8958

& -86.4792) from MODIS-Aqua radiometer

to generate time series with a spatial resolu-

tion of 4 km on the GP region and monthly-

averaged from July 2002 to March 2021. We

estimated the seasonality of the SST series with

a periodic regression with cyclic descent as

defined in Periods function by Gonzalez-Rodrí-

guez, Villalobos, Gómez-Muñoz, & Ramos

Rodríguez (2015):

where, a

, a

and a

are amplitude harmon-

ics adjustment in °C; T

and T

are the periods’

Fig. 2. Cumulative precipitation (bars), wind speed (line) and direction (arrows) monthly averages for the 2017-2019

research period, North Pacific of Costa Rica. The arrow color indicates the vector angle in reference to south.

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harmonics adjustment in months, and j

and

are phase in radians. Applying Eq.1 to the

time series, we obtained the period, ampli-

tude and lag phase of the two main harmonic

components of the SST time series (Table S1).

To obtain the anomaly signal, we subtracted

the harmonics from the original SST time

series, this subtraction removes the influence

of the annual cycle in SST series and allows

the comparison with ENSO variability. From

the resulting data, we calculated the associa-

tion between SST in GP and ENSO by doing a

cross-correlation of the filtered SST signal with

the Oceanic Niño Index (ONI) (NOAA Climate

Prediction Center).

We estimated the seasonality of the chlo-

rophyll concentration series with Periods func-

tion and with three harmonic components:

where, a

, a

and a

are amplitude harmon-

ics adjustment in chlorophyll concentration;

, T

and T

are the periods’ harmonics adjust-

ment in months, and j

, j

and j

are phase in

radians. Applying Eq. 2 to the time series, we

obtained the period, amplitude and lag phase

of the three main harmonic components of the

chlorophyll time series (Table S2). We calcu-

lated the association between chlorophyll and

SST in GP by doing a cross-correlation of the

raw monthly averaged data.

We visually evaluated the correspondence

of in-situ measurements with remote sensing

data from the MODIS-Aqua radiometer for

chlorophyll and from the GHRSST Level 4

G1SST products for sea surface temperature

(Chao, Li, Farrara, & Huang, 2009). Wind

speed, wind direction and cumulative precipita-

tion (Fig. 2) were obtained from meteorological

station #72163 of the IMN (Instituto Meteo-

rológico Nacional: National Institute of Meteo-

rology), located 315 meters above sea level in

Santa Rosa, at the northwestern flank of GP.

RESULTS

We retrieved ENSO Sea Surface Tem-

perature (SST) anomalies data for the research

period, which corresponded to La Niña condi-

tions in late 2017 and early 2018, and then

transitioned to El Niño state in late 2018 and

early 2019 (Table 1).

Vertical profile data of CTD had a depth

range from 0 to 69 m, the maximum depth

point was registered in station 9, coincid-

ing with the consulted bathymetry (Fig. 1).

Parameters ranges were: temperature 12-31

°C, salinity 30-36 g/kg, chlorophyll 0-7.5 mg/

, oxygen 0-8.5 mg/L. Results are presented

to evaluate horizontal and vertical distribution,

first the surface and bottom interpolations in all

the research area, then the vertical distribution

variation of the farthest and closest station to

the coast during the research period. In addi-

tion to this, cross-sections of GP based on

transects T1, T2 and T3 are shown for the four

TABLE 1

Warm (red) and cold (blue) periods based on a threshold of +/- 0.5 °C for the Oceanic Niño Index (ONI), based on

centered 30-year base periods updated every 5 years. Yellow boxes represent the temporal extent of this research.

Adapted from NOAA website (Climate Prediction Center Internet Team)

Year DJF JFM FMA MAM AMJ MJJ JJA JAS ASO SON OND NDJ

2015 0.6 0.6 0.6 0.8

1.0 1.2 1.5 1.8 2.1 2.4 2.5 2.6

2016

2.5 2.2 1.7 1.0 0.5

0.0 -0.3

-0.6 -0.7 -0.7 -0.7 -0.6

2017 -0.3 -0.1 0.1 0.3 0.4 0.4 0.2 -0.1 -0.4

-0.7 -0.9 -1.0

2018

-0.9 -0.8 -0.6

-0.4 -0.1 0.1 0.1 0.2 0.4

0.7 0.9 0.8

2019

0.8 0.8 0.8 0.7 0.6 0.5

0.3 0.1 0.1 0.3 0.5 0.5

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parameters. Results for the surface level are

shown in Fig. 3.

Surface observations: In all campaigns,

the horizontal distribution of temperature at

the surface showed a marked seasonal pattern

(Fig. 3A). For the three years, the temperature

was lower in the first trimester of the year and

higher during the last trimester. The coldest

temperature was recorded in February 2018,

and the warmest in September 2017; lower val-

ues were generally associated with the northern

part of GP. As for salinity, the highest values

coincide with the coldest campaign in Febru-

ary 2018 (Fig. 3B). Minimum values of salinity

(30-32 g/kg) were recorded in November 2018

in the whole study area, and in the south of GP

in February 2017 and September 2019.

Oxygen distribution was homogeneous

across GP in September 2017, while hetero-

geneity was seen on other campaigns (Fig.

3C). In February 2017, the southern flank

of GP showed values of 7 mg/L, higher than

the rest of the gulf. In November 2017 and

November 2018, high concentration values

were associated with the inner part of BC. A

local surface oxygen minimum was detected in

February 2018 between Cabuyal and Naranjo

Beach, with a concentration less than 6.5 mg/L,

while in September 2018 the minimum oxygen

values were inside BC. Chlorophyll-a concen-

tration shows a similar pattern to oxygen and

salinity, higher in the first trimester and gener-

ally decreasing over the year (Fig. 3D). Chlo-

rophyll distribution was homogenous across

GP in September 2018 and November 2018.

In February 2017, the minimum concentration

was inside BC, while the maximum was associ-

ated to the north flank, off Naranjo Beach.

In September 2017 a chlorophyll maxi-

mum was recorded in the outer part of GP

close to station 8, while in November 2017

a maximum of 2 mg/m

was present in the

inner part of BC. We recorded a particularly

high concentration of chlorophyll in February

2018, which coincided with the highest values

of salinity, in the coldest campaign and the

aforementioned site of local oxygen minimum

between Cabuyal and Naranjo Beach.

Bottom observations: We generated

bottom level interpolations to visualize the

relationships with the surface (Fig. 4). In com-

parison to the surface; we found colder waters

throughout the whole area, as expected for

tropical latitudes where temperature decreases

over depth. The temperature at the bottom

showed a similar seasonal variability to the

surface (Fig. 4A), with the lower values dur-

ing February and warmer water in September

and November. September campaigns showed

the 20 °C isotherm around the 50 m and 60 m

isobaths, with colder waters (17 °C) than the

data from November, which minimum value

recorded was 19 °C at station 17.

There was a horizontal gradient found in

all campaigns, the bottom temperature in the

inner part of BC remained always warmer than

the rest of the area, we also noted this behavior

in the northeast region of GP, in Naranjo Beach

for September, November and March. In this

regard, salinity values also coincided with the

temperature values, being lower in BC and

Naranjo Beach, associated with the stations

closer to the coast and around estuaries due to

the inputs of freshwater (Fig. 4B).

The coastal stations were generally well-

oxygenated at the bottom, with values ranging

between 4-6 mg/L (Fig. 4C). Low oxygen

values (less than 2 mg/L) were always present

in the outer part of GP, deeper than 50 m. On

the other hand, anoxic conditions (< 0.5 mg/L)

were recorded in February 2018 and September

2018-2019, farthest from the coast in February

and closest to Peninsula Papagayo and BC in

September.

The highest chlorophyll concentrations

were found in September and November, which

contrasted with low concentration values found

at the surface in these same months. Normal to

high concentrations from 0.5 to 3 mg/m

were

present in all campaigns on BC, with a particu-

lar maximum in November 2017 (Fig. 4D).

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Fig. 3. Surface distributions of Conservative Temperature (A), Absolute Salinity (B), Oxygen (C), and Chlorophyll (D) of

eight sampling in the Gulf of Papagayo, Costa Rica.

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Fig. 4. Bottom distributions of Conservative Temperature (A), Absolute Salinity (B), Oxygen (C) and Chlorophyll (D) of

eight sampling campaigns in the Gulf of Papagayo. Data for Feb-17 oxygen was invalid and not included.

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Vertical structure: We evaluated the verti-

cal structure temporal variability by comparing

the farthest and nearest to coast stations (Fig.

5). These graphs (Fig. 5) show the difference in

vertical structure among all the parameters and

give insight into the three-dimensional vari-

ability across depths. We found differences in

the vertical distribution of parameters between

stations 17 and 18. In station 18, inside BC,

the vertical structure shows a homogenous

column for temperature and salinity. On the

other hand, station 17 shows a well-defined

thermocline that shoals around 30 m in the

upwelling months.

The thermocline had the shallowest por-

tion (10-15 meters) in February 2018 (Fig.

5), associated with the maximum wind speed

recorded in the 2017-2018 period (Fig. 2). This

shows that upwelling or vertical mixing events

influence the whole area of GP while causing

the highest variation and coldest waters in the

outer parts of GP (Fig. 5A). In contrast, Fig.

5B shows a weaker stratification in coastal

stations, where values of temperature, oxygen

and chlorophyll denoted two layers over the

vertical profile, while the salinity was gener-

ally homogeneous. Temperature distribution

suggests that shallow areas inside BC could be

affected by the advection from colder waters in

the surroundings of the bay and by the vertical

mixing induced by wind stress. Tidal forcing

could influence vertical mixing, although it

was not within the scope of this study.

We recorded minimum salinity values (30-

31 g/kg) in November 2017, when the entire

water column in station 18 decreased its salini-

ty below 33 g/kg, and in contrast with values on

station 17, where low salinity was evident only

in the surface level (0-5 m). The salinity dis-

tribution, in conjunction with meteorological

data (Fig. 2), suggests that salinity descends in

GP because of runoff and river discharge, and

this could have a higher effect on the vertical

structure of coastal areas rather than outer GP.

Other factors such as advection, solar radiation

incidence and tidal forcing may also play a role

in the dynamics but were not within the scope

of this study.

The 25 °C isotherm fluctuates from 10 m

during high wind intensity to approximately 40

m in November (Fig. 5A), shoaling in BC only

during the first trimester. This isotherm coin-

cides with the chlorophyll concentration peaks.

The subsurface chlorophyll maximum shifted

between 10-15 m on station 17, and remained

at a range of four meters from the bottom inside

BC, on station 18. A maximum chlorophyll

concentration of 7.5 mg/m

was registered in

February 2018, evidencing a correspondence

between high-intensity wind periods and pri-

mary productivity peaks.

Low-oxygenated waters were associated

with high magnitude winds and predominant

80° from the north direction during the first

trimester, values less than 1 mg/L were found at

the bottom level, in outer GP below 40 m, and

inside BC below 10 m. Our results show that

the first 20 m in GP remain always well oxy-

genated. Anoxic conditions were recorded in

February 2018 and September 2018 for station

17, while inside BC values less than 0.5 mg/L

were present in September 2018 and March

2019. In general, horizontal gradients showed

similar values inside BC (stations 18-23).

To further inspect the dynamics on the

vertical dimension in GP, we visualized the

three-dimensional variability of the gulf during

September campaigns (Fig. 6): two longitu-

dinal-vertical sections that extend across BC

(T1) and off Naranjo Beach (T2), as well as a

latitudinal perspective in streamwise direction

(T3). Cross-sections are shown for the Septem-

ber campaigns.

The thermal and salinity structure indi-

cated that in September, depth gradient limits

the intrusion of colder water into the inner

parts of BC, where water in stations 20, 19 and

18 was usually warmer. North-South tempera-

ture asymmetry was identified, as the 20 °C

isotherm was shallower in the north flank of

GP, on stations that are 10-20 m deeper than

the south flank. Strong stratification happens

during September (Fig. 6A; Fig. 6B), coincid-

ing with low to moderate average wind speeds

of 1-2 m/s and low precipitation, below 200

mm of total monthly rain (Fig. 2). Based on

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Fig. 5. Time series distribution of conservative temperature, absolute salinity, dissolved oxygen and chlorophyll across depth

in the farthest and closest to coast stations (17 and 18, respectively).

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temperature, the mixed layer was wider during

September 2017 (30 m), and narrower in Sep-

tember 2019 (15 m).

The salinity vertical structure during the

rainy season showed low salinity values (< 32

g/kg) on the first 10 m of the water column

(Fig. 6B), with September 2017 showing the

lowest values. High salinity nucleus (> 34 g/

kg) was found to be associated with deeper

areas, in the north flank and outer stations

of GP, with the maximum salinity recorded

between 40-50 m in September 2018 and 2019.

Oxygen distribution in September showed

low oxygenated waters (Fig. 6C) associated

with bottom level, for the three years, although

in September 2017 minimum oxygen concen-

tration was 1 mg/L, while in September 2018

anoxic values were recorded on BC and off

Fig. 6. Longitudinal (T1, T2) and latitudinal (T3) cross-sections showing the vertical profile interpolations of conservative

temperature (A), absolute salinity (B), dissolved oxygen (C) and chlorophyll-a concentration (D) in September 2017, 2018

and 2019. Distance 0 is located on the coast.

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Cabuyal, at midwater level (40-50 m). The

anoxic layer was wider in September 2019,

when oxygen distributed asymmetrically on

GP, with higher values on the south flank

and anoxic values in the deeper areas. The

subsurface chlorophyll maximum was located

between 20-40 m in September (Fig. 6D),

with chlorophyll concentration maximum on

September 2019, inside BC near station 21. In

September 2017 the chlorophyll concentration

peak was located off Cabuyal, around 40 m

deep on the deep channel, and September 2019

showed a clear chlorophyll distribution asym-

metry with high values on the southern flank of

GP and lower values at the north flank.

SST time series retrieved from satellites

confirmed our minimum SST record in Febru-

ary 2018 and evidenced a well defined seasonal

variability in the GP region. Fig. 7 shows that

monthly averaged SST decreases in the first

Fig. 7. Longitudinal (T1, T2) and latitudinal (T3) cross-sections showing the vertical profile interpolations of conservative

temperature (A), absolute salinity (B), dissolved oxygen (C) and chlorophyll-a concentration (D) in February 2017, 2018

and March 2019. Distance 0 is located on the coast. T2 data was not available for Feb 17 and oxygen data on Feb 17 was

categorized as invalid.

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trimester and then increases in the subsequent

months (Fig. 8A), the temperature variability

range was approximate ± 2 °C. SST averages

showed that lower values coincide with strong

wind periods reported for the area during

December to March period.

The 2-harmonic analyses (Fig. 8A) of the

SST time series showed that the first harmonic

period for the region is of 12 months and ~ 0.8

°C of amplitude, while the second harmonic

period was 4 months with an amplitude of ~

0.4 °C (Table S1). Cross-correlation between

the calculated SST anomaly and ONI showed a

maximum positive correlation at 0-months time

lag. This means that the ENSO effect on SST in

GP happens immediately with no lag (P < 0.05),

confirming our results concerning the ONI

phase and in-situ surface temperature. The har-

monic analyses of chlorophyll showed the first

harmonic of 12 months, second of 18 months

and third of 15 months (Table S2). Cross-corre-

lation between chlorophyll and SST showed a

negative correlation at 0-months time lag.

DISCUSSION

The hydrographic variability of GP dur-

ing the research period confirms that seasonal

upwelling events influenced the horizontal and

vertical gradients during the first trimester.

Our results show the correspondence of sub-

surface cooling events to high wind speed as

described by Alfaro and Cortés (2012). During

the research period, wind magnitudes higher

than 2.0 m/s coincided with the colder surface

and bottom temperature values in the entire

gulf. According to Barua (2005), wind forc-

ing drives coastal upwelling, which could be

Fig. 8. Time series (2002-2021) of: (A) monthly averaged SST with two harmonic components used to obtain the anomaly

signal (periods = 12 and 4 months; R

= 0.513; P-value = 1.901e

-34

); and (B) monthly averaged chlorophyll with three

harmonic components (periods = 12, 18 and 15 months; R

= 0.316; P-value = 1.376e

-16

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associated with three different processes that

apply to GP context, in relation to the geomor-

phology of the coast and its interaction with

wind fields: alongshore wind, offshore/onshore

wind and open ocean divergence/convergence.

Results showed a predominant northeast-

erly wind direction (60-90°), which partially

satisfies the alongshore wind condition in

the northern and southern flank of GP. At the

north, the Peninsula de Papagayo coastline

extends in a SE-NW direction, with small bays,

river mouths and cliffs that could experiment

downwelling as they are upward from the wind

direction. On the other hand, the southern flank

extends on a NE-SW, parallel to the wind direc-

tion and thus fulfilling the condition for along-

shore upwelling. In this regard, upwelling in

GP could be further influenced by the offshore

wind that blows perpendicular to the coast, as

the section from Cabuyal to Naranjo Beach

fulfills this condition; this was proved by our

results based on temperature and chlorophyll

concentration distribution. The third underlying

mechanism of the observed upwelling could be

the open ocean divergence represented by the

CRTD. Although some of these aspects can be

inferred from the data collected in this study,

the validation of these hypotheses must be

inspected further through ADCP mooring data

and wind field cross-correlation products.

Although the three upwelling periods in

our records have shown a reduction in tempera-

ture, February 2017 showed warmer values at

the surface level which could be attributed to

weaker winds than in February of 2018 and

2019. In contrast, March’s bottom temperature

in 2019 was warmer than in the other years,

during the positive ENSO phase. During the

research period, the temperature inside BC was

warmer than the rest of the gulf.

The three ENSO phases were present

during the research period. First, a strong “La

Niña” event from October 2017 to March 2018

cooled down the waters to 12 °C at the bottom

of GP, probably because of stronger winds

(Wang & McPhaden, 2001). In contrast, the

“El Niño” event that took place from October

2018 until June 2019 was associated with the

warmest waters of all the September cam-

paigns. When we compare the first trimester of

the three years, for 2017 it was in the neutral

phase of ENSO while 2018 was negative and

2019 was a positive phase. The latter being the

warmest upwelling period at the bottom level.

Although bottom water was below 15 °C in GP

in February 2017, inside BC the temperature

remained warmer than the rest of the gulf. We

suggest this could be caused by low magnitude

winds in the first months of 2017, with an aver-

age speed not surpassing 2.5 m/s, while 2018

and 2019 showed values higher than 3.0 m/s,

this could have lead to reduced vertical mixing

inside BC. Based on these facts, we suggest

that a wind magnitude threshold of 3 m/s could

lead to the shoaling of the thermocline in the

inner part of BC. These results confirm the

important effects of ENSO on the interannual

variability (Marrari, Piola, & Valla, 2017)

Observations of seawater temperature con-

firm that the Gulf of Papagayo experiences

significant seasonal differences, based on con-

trasting values associated with strong winds

during the first trimester (Jiménez, 2001) and

the rainy season in the third and fourth trimes-

ter. The heterogeneity in the horizontal distri-

bution of properties shows that these upwelling

events may have different extents and effects

inside BC, where bathymetry seems to play

an important role in local circulation, as well

as the solar radiation incidence on shallower

areas, horizontal advection with surrounding

waters of GP and vertical mixing by wind and/

or tidal forcing. The evidence found suggests

that the hydrography and circulation in shal-

lower areas like in BC could be dominated by

vertical mixing and tides, while deeper areas in

outer GP could be more influenced by upwell-

ing processes.

Time-series analyses showed that season-

ality is well defined for the GP area, meaning

that winds have a strong influence on the evolu-

tion of SST along the year (Alfaro et al., 2012).

Cross-correlation results confirmed the direct

association between SST and ENSO phase (lag

0, P < 0.05) and SST with chlorophyll (lag 0,

P < 0.05), coinciding with annual variability of

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in-situ observations and with previous studies

done by Alfaro and Lizano (2001), who calcu-

lated a significant lag of ~2 months through the

decomposition of a 50-year SST time series.

This means that ENSO is the main influence

over the Northeastern Tropical Pacific, with

positive correlations with no delay. Although

the ENSO effect was confirmed, the two-

harmonic model only explains ~ 60 % of the

time series, on this regard, it has been indicated

that this area is subject to another synoptic-

scale variability such as Kelvin waves, the

Pacific Decadal Oscillations, ATN and ATS

oscillations (Alfaro & Lizano, 2001; Jia, Chen,

& Zuo, 2017; Trasviña, Lluch, Filonov, &

Gallegos, 1999). Chlorophyll showed a signifi-

cant inverse correlation with SST, confirming

in-situ results.

A visual evaluation of the spatial patterns

of chlorophyll-a concentration and its relation-

ship with CRTD was done through a visual

comparison of the collected data, and satellite

data for the specific dates when sampling was

done. February 2017 range of values coincided

with the satellite measurements for GP (Fig.

S1), specifically with values greater than 3

mg/m

at the north flank of GP. Satellite data

for September 2017 were not available for

the extension of GP, probably due to weather

conditions. November 2017 satellite-derived

chlorophyll concentration range and distribu-

tion also coincided with in-situ measurements.

In February 2018, during the upwelling period,

we recorded anomalous concentration values

that corresponded to a negative anomaly value

of the ENSO index. The subsequent months

of 2018 match the in-situ concentrations, both

showing a low concentration all over GP and

throughout 87 °W. In March 2019, satellite-

derived values indicated low chlorophyll con-

centration, opposite to in-situ data that showed

surface concentrations up to 2 mg/m

The difference in values of chlorophyll-a

concentration may be attributed to the tempo-

ral resolution of the visually compared data,

as CTD data were only measured once while

satellite data shows weekly averaged values.

Based on this, we suggest that for March 2019,

in-situ data could have recorded a short-lived

event caused by the off-shore wind blowing

and thus, it was not reflected on the satellite

weekly average. Another explanation could

be attributed merely to the optics nature of

the sensors compared, as the CTD fluores-

cence sensor captures different signals than

the MODIS-Aqua radiometer. In this regard,

Salyuk et al. (2010) indicate that fluorometers

could have large errors in coastal waters where

rivers and anthropogenic activity impact the

concentration of Dissolved Organic Matter

(DOM), affecting the optical accuracy of mea-

surements as chlorophyll-a fluorescence signal

mixes with the DOM signal.

SST data from GP surrounding waters

was retrieved through a longitudinal section of

approximately 130 km offshore GP (Fig. S2).

This data shows a pattern of low temperature

during the first trimester and higher tempera-

tures over the rest of the year, matching in-situ

results obtained in GP. The interannual vari-

ability detected from satellite sensors showed

warmer SST for the first trimester of 2017, in

comparison to 2018 and 2019. Although this is

supported by our data, it is important to note

that satellite data indicated lower SST values

in January and March 2017, which could be

influenced by low wind stress in that month

(monthly average less than 2.0 m/s). In Fig.

S2, lines 1, 4 and 7 represent upwelling period

sampling, which can be appreciated by cold

water extending from 87 °W all over to GP.

For the first trimester of 2018, a large spatio-

temporal extension of cold waters below 23 °C

was detected during ENSO negative anomaly

(-0.8) from -87.0 to -86.30, extending further

eastward in comparison to 2017 and 2019. The

minimum temperature values in February 2018

coincided with in-situ data of GP. We suggest

that ENSO negative phase increased the exten-

sion of low SST values. The low SST can also

be associated with the CRTD and its interac-

tion with the continental shelve and coastal

areas, nevertheless, this remains to be answered

through exhaustive research. Additionally, this

figure shows how the SST increased during the

El Niño period of 2018-2019. Considering the

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limitations of our data and the superposition

of different physical processes, we could not

develop an accurate interpretation of cause

and effect for the observed results in GP and

its relation to regional conditions, especially as

the coupled ocean-atmosphere system affects

biological processes which can also modify

the low and high-frequency variability. Despite

this fact, we consider that wind intensifica-

tion leads to an interaction between upwelled

coastal waters and the CRTD, probably in the

form of anticyclonic rings that transport water

off Papagayo in a northwestward direction

(Vargas, 2002). Previous studies have indicated

that the upwelling plumes of Papagayo block

the northward flow of the Costa Rica Coastal

Current (CRCC), attributing the formation of

Papagayo eddies to the conservation of poten-

tial vorticity of the CRCC when it interacts

with sustained forcing by the wind (Ballestero

& Coen, 2004).

Upwelling is in many parts of the Eastern

Tropical Pacific an important factor to local

dynamics (Fiedler & Lavin, 2017). Based

on the data collected on this research, the

GP shows a similar variability to the Gulf of

Panama. In both places, a seasonal upwelling

has been associated with the annual migration

of the Intertropical Convergence Zone (ITCZ)

(Poveda, Waylen, & Pulwarty, 2006). From

December to mid-April, the ITCZ migrates

south of the Isthmus of Panama, intensifying

the northeast trade winds across the region

and bringing cold, nutrient-rich, deep water up

and onto the shelf (D’Croz & O’Dea, 2007).

Such wind-driven upwelling events can reduce

SST in the Gulf of Panama by 10 °C within

a few days to weeks, and this also coincides

with bottom temperature in GP, where tem-

perature values can drop by 15 °C in the outer

part of the gulf.

Along with cold waters, a slight shoal-

ing of the oxycline to depths of around 45 to

50 m occurred especially during the negative

ENSO phase in 2018 and the upwelling season.

While the vertical migration of the oxycline

can take place in any stratified ocean region,

the minimum concentration of < 1 mg/L could

be attributed to the influence of the Oxygen

Minimum Zone of the ETP, which has its wider

vertical extension around the CRTD (Fiedler &

Lavin, 2017). The Costa Rica Dome is similar

to other tropical thermocline domes in several

aspects: it is part of an east-west thermocline

ridge associated with the equatorial circulation,

surface currents flow cyclonically around it,

and its seasonal evolution is affected by large-

scale wind patterns. The Costa Rica Dome is

unique because it is also forced by a coastal

wind jet. A seasonally predictable, strong, and

shallow thermocline makes the Costa Rica

Dome a distinct biological habitat that provides

important ecosystem services on a regional and

global scale (Johnson et al., 2018).

Primary productivity was in general mod-

erate to high in GP, compared to previous

studies conducted in the area (Álvarez et al.

2018; Ruiz, 2018) that registered chlorophyll-a

concentrations above 0.5 mg/m

all year over.

The chlorophyll peak values coincided with

the depth of the 25°C isotherm. During the

ENSO negative phase, chlorophyll values were

considerably higher, confirming the results of

measurements and numerical models run for

the Eastern Tropical Pacific which predict La

Niña conditions boost the primary production

as the chlorophyll levels are related to changes

in the supply of nitrate rich-waters through

vertical mixing and upwelling (Marrari et al.,

2017; Sasai, Richards, Ishida, & Sasaki, 2012).

The subsurface chlorophyll maximum, usually

located at depths of 35 m in September, disap-

peared during the upwelling periods to make

way to a vertically homogeneous distribution in

the most superficial layer of the water column

with higher values, suggesting the intrusion of

subsurface waters from deeper levels towards

the surface (above 20 m depth) and the role of

vertical mixing induced by wind. This homoge-

neity of the most superficial levels in the first

trimester of the year reflects how the absence

of lateral sources of freshwater, turbulent mix-

ing induced by the wind and upwelling pro-

cesses are the modulating factors of the vertical

structure of the water column during the dry

period (Álvarez et al., 2018).

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The minimum salinity of station 18 was

in November 2017, matching weather station

data in which maximum precipitation occurred

over the last trimester of 2017. This suggests

that river discharge and runoff influence the

salinity in GP and also that advection from

the Tropical Surface Water mass (TSW) could

be influencing the dynamics inside GP. TSW

is characterized in this region of the ETP for

having salinities less than 34 PSU and tem-

peratures above 25 °C (Brenes, Kwiecinski,

D’Croz, & Chávez, 1995), due to the excess

of precipitation over evaporation in this region

and high solar radiation incidence throughout

the year (Amador et al., 2016).

Comparing our results to surrounding areas

within the upwelling influence region, such as

Golfo de Santa Elena, there is a clear differ-

ence in the chlorophyll ranges. For example,

in September, values in GP are usually lower

than the ones reported in Bahía Santa Elena

that can go up to 1.5 mg/m

(Tisseaux-Navarro,

Salazar-Ceciliano, Cambronero-Solano, Var-

gas-Hernández, & Marquez, 2021). In the outer

parts of Golfo de Santa Elena, chlorophyll

concentrations show similar maximum values

of 7.5 mg/m

on upwelling periods (Ballestero,

Murillo, Vargas, & Tisseaux, 2017). Although

GP is an environment influenced by coastal

upwelling, primary productivity is not as high

as in Golfo de Santa Elena, which can be attrib-

uted to the wind magnitude which is reduced in

GP by the Peninsula de Papagayo mountains in

the Santa Rosa National Park, which appears

to block part of the trade winds from NE direc-

tion. Another aspect that could explain the

difference between these adjacent gulfs is the

bathymetry and the coastline orientation rela-

tive to prevailing wind direction.

We recommend generating extended time-

series data by installing fixed pressure sensors

or ADCP moorings to compare with wind data

to better understand its effects on the hydro-

graphic variability and circulation in GP. Since

GP is the birth of the CRTD, understanding

its dynamics means a better understanding of

the CRTD and the Eastern Tropical Pacific

Oxygen Minimum Zone effects in coastal

waters, which could eventually input better

management of fisheries and living resources

in the Costa Rican Exclusive Economic Zone

(Johnson et al., 2018).

Ethical statement: authors declare that

they all agree with this publication and made

significant contributions; that there is no con-

flict of interest of any kind; and that we fol-

lowed all pertinent ethical and legal procedures

and requirements. All financial sources are

fully and clearly stated in the acknowledge-

ments section. A signed document has been

filed in the journal archives.

See Digital Appendix at: revistas.ucr.ac.cr

ACKNOWLEDGMENTS

To Vicerrectoría de Investigación, Uni-

versidad Nacional for the project funding and

Fundación MarViva for the financial support

with research vessels.

RESUMEN

Variabilidad hidrográfica en el Golfo de Papagayo

durante el periodo 2017-2019

Introducción: El Golfo de Papagayo (GP) es un sitio de

alta importancia socioeconómica ubicado en el Pacifico

Norte de Costa Rica. Los servicios ecosistémicos de este

sitio representan un beneficio a las comunidades locales, y

su dinámica está influenciada por un sistema de surgencia

costera que influye en la actividad pesquera y comercial.

Objetivo: El objetivo de este estudio fue caracterizar la

variabilidad espacio-temporal de los principales paráme-

tros hidrográficos a través de mediciones in situ durante el

período 2017-2019.

Metodología: Se realizaron 8 campañas de medición,

donde se desplegó una sonda CTD para realizar perfiles

verticales en 23 estaciones distribuidas en todo el GP, para

caracterizar las variaciones de temperatura, salinidad, oxí-

geno disuelto y concentración de clorofila.

Resultados: En el primer período del año se encontró una

temperatura mínima de superficie y fondo asociada a la

surgencia causada por el viento. El aumento de salinidad

estuvo asociado a la disminución en la temperatura, siendo

su valor más alto en el primer período del año y dismi-

nuyendo hasta alcanzar un mínimo en Noviembre. Los

valores más altos de clorofila estuvieron relacionados con

las temperaturas más bajas en superficie y los valores más

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bajos de oxígeno con las temperaturas más bajas en fondo.

Se caracterizó la hidrografía de Bahía Culebra en relación

con la parte externa de GP.

Conclusiones: La batimetría determina una asimetría sur-

norte de salinidad y temperatura. Los eventos de enfria-

miento subsuperficiales coinciden con períodos de fuertes

vientos. La surgencia influye en la dinámica hidrográfica

de superficie y fondo en GP y determina la variabilidad

interanual. El evento La Niña de 2018 mostró el período

de surgencia más fuerte, posiblemente promoviendo la

interacción de las aguas costeras y el Domo Térmico de

Costa Rica.

Palabras clave: afloramiento costero; Pacífico Tropical

Oriental; hidrografía; ENOS; Golfo de Papagayo.

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