Article

The annual cycle and biological effects of the Costa Rica Dome

NOAA/National Marine Fisheries Service (NMFS), Southwest Fisheries Science Center, P.O. Box 271, La Jolla, CA 92038, USA
Deep Sea Research Part I Oceanographic Research Papers (Impact Factor: 2.57). 02/2002; 49(2):321-338. DOI: 10.1016/S0967-0637(01)00057-7

ABSTRACT

The Costa Rica Dome is similar to other tropical thermocline domes in several respects: 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. Monthly climatological fields of thermocline depth and physical forcing variables (wind stress curl and surface current divergence) were analyzed to examine the structure and seasonal evolution of the dome. The annual cycle of the dome can be explained by wind forcing in four stages: (1) coastal shoaling of the thermocline off the Gulf of Papagayo during February–April, forced by Ekman pumping on the equatorward side of the Papagayo wind jet; (2) separation from the coast during May–June when the intertropical convergence zone (ITCZ) moves north to the countercurrent thermocline ridge, the wind jet stops, and the North Equatorial Countercurrent extends toward the coast on the equatorward flank of the ridge; (3) countercurrent thermocline ridging during July–November, when the dome expands to the west as the countercurrent thermocline ridge shoals beneath a band of cyclonic wind stress curl on the poleward side of the ITCZ; and (4) deepening during December–January when the ITCZ moves south and strong trade winds blow over the dome. Coastal eddies may be involved in the coastal shoaling observed during February–March. A seasonally predictable, strong, and shallow thermocline makes the Costa Rica Dome a distinct biological habitat where phytoplankton and zooplankton biomass are higher than in surrounding tropical waters. The physical structure and biological productivity of the dome affect the distribution and feeding of whales and dolphins, probably through forage availability.

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    • "Several connections can be made among the experiments based on study design and subsequent hydrographic analysis . Cycles 2 and 4 were clearly in the central dome region, and Cycle 3 also fits the criterion for being in the dome region, with the 208C isotherm at 35 m (Fiedler, 2002). Cycle 5 was located out of the dome region, but had T-S properties closely resembling Cycle 4 (Landry et al., 2015a). "
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    ABSTRACT: We investigated biomass and composition of heterotrophic microbes in the Costa Rica Dome during June–July 2010 as part of a broader study of plankton trophic dynamics. Because picophytoplankton (<2 μm) are known to dominate in this unique upwelling region, we hypothesized tight biomass relationships between size-determined predator–prey pairs (i.e. picoplankton–nano-grazers, nanoplankton–micro-grazers) within the microbial community. Integrated biomass of heterotrophic bacteria ranged from 180 to 487 mg C m−2 and was significantly correlated with total autotrophic carbon. Heterotrophic protist (H-protist) biomass ranged more narrowly from 488 to 545 mg C m−2, and was comprised of 60% dinoflagellates, 30% other flagellates and 11% ciliates. Nano-sized (<20 μm) protists accounted for the majority (57%) of grazer biomass and were positively correlated with picoplankton, partially supporting our hypothesis, but nanoplankton and micro-grazers (>20 μm) were not significantly correlated. The relative constancy of H-protist biomass among locations despite clear changes in integrated autotrophic biomass, Chl a, and primary production suggests that mesozooplankton may exert a tight top-down control on micro-grazers. Biomass-specific consumption rates of phytoplankton by protistan grazers suggest an instantaneous growth rate of 0.52 day−1 for H-protists, similar to the growth rate of phytoplankton and consistent with a trophically balanced ecosystem dominated by pico-nanoplankton interactions.
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    • "Phytoplankton productivity and biomass in the CRD is highest during the summer leading to elevated zooplankton biomass, which presumably attracts the schools of blue whales that frequent the area (Fiedler, 2002). However, even when chlorophyll is elevated, this area has relatively high concentrations of unutilized macronutrients compared with adjacent oligotrophic regions (Broenkow, 1965; Fiedler, 2002; Ahlgren et al., 2014), suggesting the presence of high nutrient-low chlorophyll conditions (Minas et al., 1986). Dissolved Fe concentrations in surface waters are low enough to limit both eukaryotes and Synechococcus (Ahlgren et al., 2014). "
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    ABSTRACT: Mineral limitation of mesozooplankton production is possible in waters with low trace metal availability. As a step toward estimating mesozooplankton Fe and Zn requirements under such conditions, we measured tissue concentrations of major and trace nutrient elements within size-fractioned zooplankton samples collected in and around the Costa Rica Upwelling Dome, a region where phytoplankton growth may be co-limited by Zn and Fe. The geometric mean C, N, P contents were 27, 5.6 and 0.21 mmol gdw−1, respectively. The values for Fe and Zn were 1230 and 498 nmol gdw−1, respectively, which are low compared with previous measurements. Migrant zooplankton caused C and P contents of the 2–5 mm fraction to increase at night relative to the day while the Fe and Zn contents decreased. Fe content increased with size while Zn content decreased with size. Fe content was strongly correlated to concentrations of two lithogenic tracers, Al and Ti. We estimate minimum Fe:C ratios in large migrant and resident mixed layer zooplankton to be 15 and 60 µmol mol−1, respectively. The ratio of Zn:C ranged from 11 µmol mol−1 for the 0.2–0.5 mm size fraction to 33 µmol mol−1 for the 2–5 mm size fraction.
    No preview · Article · Dec 2015 · Journal of Plankton Research
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    • "I N T RO D U C T I O N The Costa Rica Dome (CRD) is an open-ocean upwelling system driven by wind stress curl associated with the Papagayo wind jet (Hofmann et al., 1981; Fiedler, 2002). This wind pattern causes uplift of isopycnals and a shoaling of the already shallow Eastern Tropical Pacific (ETP) thermocline in the region of 98N, 908W, which introduces new nutrients into the euphotic zone and stimulates primary production. "
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    ABSTRACT: The Costa Rica Dome is a picophytoplankton-dominated, open-ocean upwelling system in the Eastern Tropical Pacific that overlies the ocean's largest oxygen minimum zone. To investigate the efficiency of the biological pump in this unique area, we used shallow (90–150 m) drifting sediment traps and 234Th:238U deficiency measurements to determine export fluxes of carbon, nitrogen and phosphorus in sinking particles. Simultaneous measurements of nitrate uptake and shallow water nitrification allowed us to assess the equilibrium balance of new and export production over a monthly timescale. While f-ratios (new:total production) were reasonably high (0.36 ± 0.12, mean ± standard deviation), export efficiencies were considerably lower. Sediment traps suggested e-ratios (export/14C-primary production) at 90–100 m ranging from 0.053 to 0.067. ThE-ratios (234Th disequilibrium-derived export) ranged from 0.038 to 0.088. C:N and N:P stoichiometries of sinking material were both greater than canonical (Redfield) ratios or measured C:N of suspended particulates, and they increased with depth, suggesting that both nitrogen and phosphorus were preferentially remineralized from sinking particles. Our results are consistent with an ecosystem in which mesozooplankton play a major role in energy transfer to higher trophic levels but are relatively inefficient in mediating vertical carbon flux to depth, leading to an imbalance between new production and sinking flux.
    Full-text · Article · Nov 2015 · Journal of Plankton Research
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