Coastal upwelling

Thermocline-dwelling foraminifera calcify over a depth range of several hundred meters; analysis of individual shells therefore allows insight to the hydrography of the upper water column. We analyzed δ 18 O, δ 13 C, and Mg/Ca of individual tests of the planktonic foraminifera Globorotalia inflata from a sediment core (GeoB7926-2) obtained from 20°N in the eastern tropical Atlantic. To facilitate sample throughput, tests were cleaned before Mg/Ca analysis using a pipette robot. The eight samples came from five time periods with contrasting climate states. Median reconstructed temperatures were lowest during the warmth of the Bølling Allerød BA) (11.8°C), while highest temperatures (>14°C) were recorded during the cold periods of the Last Glacial Maximum (LGM), late Heinrich Stadial 1 (HS1), and the Younger Dryas (YD). Southward shift in the subtropical gyre during Northern Hemisphere cold periods and modulation by upwelling could explain the temperature change but not all of the salinity change. δ 18 O seawater-IVC indicated that salinity was higher than the global average during the LGM, with very high salinity excursions in HS1 and a smaller excursion in the YD. The upwelling signature was most strongly imprinted on range in δ 13 C. The large changes in salinity and δ 13 C between time slices cannot be explained by upwelling intensity but indicate the presence of a very saline water mass, with low δ 13 C, in the eastern North Atlantic subsurface during Northern Hemisphere cold periods.

Using the long-term wind time series, coastal upwelling was investigated in the northern Persian Gulf. The shoreline was divided into 34 segments from NW to SE and the daily Ekman transport components were computed. Based on the Ekman transport components, a coastal upwelling index was calculated. Starting from these, in this paper we present, for the fi rst time in this region, the annual cycles of the coastal upwelling. The annual cycles revealed the most intense coastal upwelling in the central areas, located about 51˚E51˚E-53˚E53˚E, including three peaks in June, November and February. In addition, a simple optimization procedure has been done to determine the best shoreline angle for the favourable conditions of coastal upwelling occurrence at each segment and month. To investigate the results, sea surface temperature (SST) and sea level anomalies (SLAs) were analysed. A cross-correlation analysis was done on the daily time series and indicated that the SST decreases more in the segments with more intense coastal upwelling along the northern shoreline. The linear temporal trend was also applied to SLA gridded time series; the results show the sea level anomaly responses to wind-driven coastal upwelling.

Continuous multiyear records of sediment-trap-gained microorganism fluxes are scarce. Such studies are important to identify and to understand the main forcings behind seasonal and multiannual evolution of microorganism flux dynamics. Here, we assess the long-term flux variations and population dynamics of diatoms, coccolithophores, cal-careous and organic dinoflagellate cysts, foraminifera and pteropods in the eastern boundary upwelling ecosystem of the Canary Current. A multiannual, continuous sediment trap experiment was conducted at the mooring site CBeu (Cap Blanc eutrophic; ∼ 20 • N, 18 • W; trap depth is ca. 1300 m) off Mauritania (northwest Africa), between June 2003 and March 2008. Throughout the study, the reasonably consistent good match of fluxes of microorganisms and bulk mass reflects the seasonal occurrence of the main upwelling season and relaxation and the contribution of microorganisms to mass flux off Mauritania. A clear successional pattern of microorganisms, i.e., primary producers followed by secondary producers, is not observed. High fluxes of diatoms, coccolithophores, organic dinoflagellate cysts, and plank-tonic foraminifera occur simultaneously. Peaks of calcare-ous dinoflagellate cysts and pteropods mostly occurred during intervals of upwelling relaxation. A striking feature of the temporal variability of population occurrences is the persistent pattern of seasonal groups contributions. Species of planktonic foraminifera, diatoms, and organic dinoflagellate cysts typical of coastal upwelling, as well as cooler-water planktonic foraminifera and the coccolithophore Gephyro-capsa oceanica, are abundant at times of intense upwelling (late winter through early summer). Planktonic foraminifera and calcareous dinoflagellate cysts are dominant in warm pelagic surface waters, and all pteropod taxa are more abundant in fall and winter when the water column stratifies. Similarly , coccolithophores of the upper and lower photic zones, together with Emiliania huxleyi, and organic dinoflagellate cysts dominate the assemblage during phases of upwelling relaxation and deeper layer mixing. A significant shift in the "regular" seasonal pattern of taxa relative contribution is observed between 2004 and 2006. Benthic diatoms strongly increased after fall 2005 and dominated the diatom assemblage during the main upwelling season. Additional evidence for a change in population dynamics is the short dominance of the coccolithophore Umbili-cosphaera annulus, the occurrence of the pteropod Limacina bulimoides and the strong increase in the flux of calcareous dinoflagellate cysts, abundant in warm tropical oligotrophic waters south of the study area after fall 2005. Altogether, this suggests that pulses of southern waters were transported to the sampling site via the northward Mauritania Current. Our multiannual trap experiment provides a unique opportunity Published by Copernicus Publications on behalf of the European Geosciences Union. 188 O. E. Romero et al.: Plankton variability off Mauritania to characterize temporal patterns of variability that can be extrapolated to other eastern boundary upwelling ecosystems (EBUEs), which are experiencing or might experience similar future changes in their plankton community.

Corals of the eastern tropical Pacific live in a marginal and oceanographically dynamic environment. Along the Pacific coast of Panamá, stronger seasonal upwelling in the Gulf of Panamá in the east transitions to weaker upwelling in the Gulf of Chiriquí in the west, resulting in complex regional oceanographic conditions that drive differential coral‐reef growth. Over millennial timescales, reefs in the Gulf of Chiriquí recovered more quickly from climatic disturbances compared with reefs in the Gulf of Panamá. In recent decades, corals in the Gulf of Chiriquí have also had higher growth rates than in the Gulf of Panamá. As the ocean continues to warm, however, conditions could shift to favor the growth of corals in the Gulf of Panamá, where upwelling may confer protection from high‐temperature anomalies. Here we describe the recent spatial and temporal variability in surface oceanography of nearshore environments in Pacific Panamá and compare those conditions with the dynamics of contemporary coral‐reef communities, during and after the 2016 coral‐bleaching event. Although both gulfs have warmed significantly over the last 150 years, thermal maxima in the Gulf of Chiriquí are increasing faster, and ocean temperatures there are becoming more variable than in the recent past. In contrast to historical trends, we found that coral cover, coral survival, and coral growth‐rates were all significantly higher in the Gulf of Panamá. Corals bleached extensively in the Gulf of Chiriquí following the 2015–2016 El Niño event, whereas upwelling in the Gulf of Panamá moderated the high temperatures caused by El Niño, allowing the corals largely to escape thermal stress. As the climate continues to warm, upwelling zones may offer a temporary and localized refuge from the thermal impacts of climate change, while reef growth in the rest of the eastern tropical Pacific continues to decline.

Sixteen years of sea surface temperature (SST, 1994-2009) were used to characterize the southern Caribbean upwelling system. This system extends from 61-75.51W and 10-12.51N, with 21 upwelling foci clustered in seven groups differentiated by their SST cycles. Two of those groups had the strongest coastal upwelling: the 'eastern area' (63-651W) and the 'western area' (70-731W). The literature reports that the eastern and western upwelling areas hold 78% and 18% of the small pelagic biomass within the upwelling system, respectively. We looked into variations of the upwelling dynamics in those areas using seasonal cycles of satellite SST, chlorophyll-a (Chl) and sea-wind, as well as climatological hydrographic data from the World Ocean Atlas. Comparing their annual averages, the eastern area featured the lowest SST (25.24 1C) and the highest Chl (1.65 mg m −3); it has moderate wind intensity (6.12 m s −1) and shallower 22 1C isotherm (85 m). The western area had stronger winds (8.23 m s −1) but deeper 22 1C isotherm (115 m), slightly higher SST (25.53 1C) and moderate Chl (1.15 mg m −3). The upwelling in the eastern area was more prolonged than in the western area (SST o26 1C during 8.5 and 6.9 months, respectively). According to the 'optimal environmental window' theory, small clupeoid recruitment is a dome-shaped function of the upwelling intensity, turbulence and SST, with an optimum wind speed around 5-6 m s −1. The eastern upwelling area wind speed is close to this optimum value. The western upwelling area shows much higher wind speed that causes high level of turbulence and strong offshore transport that could hinder small pelagics recruitment in that area.

The southern Caribbean Sea experiences strong coastal upwelling between December and April due to the seasonal strengthening of the trade winds. A second upwelling was recently detected in the southeastern Caribbean during June-August, when local coastal wind intensities weaken. Using synoptic satellite measurements and in situ data, this midyear upwelling was characterized in terms of surface and subsurface temperature structures, and its mechanisms were explored. The midyear upwelling lasts 6-9 weeks with satellite sea surface temperature (SST) ~1-2 • C warmer than the primary upwelling. Three possible upwelling mechanisms were analyzed: cross-shore Ekman transport (csET) due to alongshore winds, wind curl (Ekman pumping/suction) due to wind spatial gradients, and dynamic uplift caused by variations in the strength/position of the Caribbean Current. These parameters were derived from satellite wind and altimeter observations. The principal and the midyear upwelling were driven primarily by csET (78-86%). However, SST had similar or better correlations with the Ekman pumping/suction integrated up to 100 km offshore (W E 100) than with csET, possibly due to its influence on the isopycnal depth of the source waters for the coastal upwelling. The midyear upwelling was not caused by dynamic uplift but it might have been enhanced by the seasonal intensification of the Caribbean Current during that period.

Long-term data characterizing the oceans' biological carbon pump are essential for understanding impacts of climate variability on marine ecosystems. The "Bakun upwelling intensification hypothesis" suggests intensified coastal upwelling due to a greater land-sea temperature gradient influenced by global warming. We present long time series of bathypelagic (approximately 1,200-3,600 m) particle fluxes from a coastal (CBeu: 2003-2016) and an offshore (CBmeso: 1988-2016) sediment trap setting located in the Canary Current upwelling. Organic carbon (C org) and biogenic opal (BSi, diatoms) fluxes were twofold to threefold higher at the coastal upwelling site compared to the offshore site, respectively, and showed higher seasonality with flux maxima in spring. A relationship between winter and spring BSi fluxes to the North Atlantic Oscillation index was best expressed at the offshore site CBmeso. Lithogenic (dust) fluxes regularly peaked in winter when frequent low-altitude dust storms and deposition occurred, decreasing offshore by about threefold. We obtained a high temporal match of short-term peaks of BSi and dust fluxes in winter to spring at the inner site CBeu. We found synchronous flux variations at both sites and an anomalous year 2005, characterized by high BSi and C org fluxes under a low North Atlantic Oscillation. C org and BSi fluxes revealed a decreasing trend from 2006 to 2016 at the coastal site CBeu, pointing to coastal upwelling relaxation during the last two decades. The permanent offshore upwelling zone of the deflected Canary Current represented by the flux record of CBmeso showed no signs of increasing upwelling as well which contradicts the Bakun hypothesis.

Continuous multiyear records of sediment trap-gained microorganism fluxes are scarce. Such studies are important to identify and to understand the main forcings behind seasonal and multiannual evolution of microorganism flux dynamics. Here, we assess the long-term flux variations and population dynamics of diatoms, coccolithophores, calcareous and organic dinoflagellates, foraminifera and pteropods in the Eastern Boundary Upwelling Ecosystem (EBUE) of the Canary Current. A multiannual, continuous sediment trap experiment was conducted at the mooring site CB eu (Cape Blanc eutrophic, ~20°N, 18°W; trap depth = ca. 1,300 m) off Cape Blanc, Mauritania (northwest Africa), between June 2003 and March 2008. Throughout the study, the reasonably consistent good match of fluxes of microorganisms and bulk mass reflects the seasonal occurrence of the main upwelling season and the contribution of microorganisms to mass flux off Mauritania. A clear successional pattern of microorganisms, i.e. primary producers followed by secondary producers, is not observed. High fluxes of diatoms, coccolithophores, organic dinoflagellates cysts, and planktonic foraminifera occur simultaneously. Peaks of calcareous dinoflagellate cysts and pteropods mostly occurred during intervals of upwelling relaxation. A striking feature of the temporal variability of populations' occurrence is the persistent pattern of seasonal groups' contribution. Species of planktonic foraminifera, diatom, and organic dinoflagellate cysts typical of coastal upwelling as well as cooler water planktonic foraminifera and the coccolithophore Gephyrocapsa oceanica are abundant at times of intense upwelling (late winter through early summer). Planktonic foraminifera and calcareous dinoflagellate cysts dominant in warm pelagic surface waters and all pteropod groups are more abundant in fall and winter, when the mixed layer deepens. Similarly, coccolithophores of the upper-and lower photic zone, together with Emiliania huxleyi, and organic dinoflagellate cysts dominate the assemblage during phases of upwelling relaxation and deeper layer mixing. A significant shift in the 'regular"' seasonal pattern of species relative contributions is observed between 2004 and 2006. Benthic diatoms strongly increased after fall 2005 and dominated the diatom assemblage during main upwelling season. Additional evidence for a change in population dynamics are the short dominance of the coccolithophore Umbilicosphaera annulus, the occurrence of the pteropod Limacina bulimoides, and the strong increase in the flux of calcareous dinoflagellate cysts, abundant in tropical, warm oligotrophic waters south of the research area after fall 2005. Altogether, this suggests that pulses of southern waters were transported to the sampling site via the northward Mauritania Current. Our multiannual trap experiment provides a unique opportunity to characterize temporal patterns of variability that can be extrapolated to other 48 EBUEs, which are experiencing or might experience similar future changes in the plankton community.

Nearshore ichthyoplankton assemblages are constantly influenced by the dynamics of coastal environments (i.e. daily thermal gradients and coastal currents), as well as by regional environmental forcing, such as upwelling events. The aims of this study were to describe larval and postlarval fish assemblages on a short-time scale and relate their intra-and interannual fluctuations to local (< 1 km) and regional (~ 40 km) oceanographic conditions, at two locations of central Chile (Montemar and El Quisco), 50 km distant from each other. Environmentally, spring-summer 2015-2016 was more stable than spring-summer 2016-2017, evidencing weaker temperature fluctuations. In addition, the first season of the study showed positive temperature anomalies that agree with the warm phase of El Niño-Southern Oscillation (ENSO) 2015. Both larval abundance (29,090 ind. 100 m −3 period 1; 23,100 ind 100 m −3 period 2) and postlarval CPUE (6.8 ind. light trap −1 night −1 period 1; 4.8 ind. light trap −1 night −1 period 2) decreased in the second period of study. The structure of the larval assemblages was significantly related to seawater temperature and wind regime, and showed seasonal fluctuations in the abundance, with higher densities in spring, and lower in summer, while postlarval assemblages did not relate significantly to any physical variable. At the interannual scale, the stability of the water column probably promotes fish reproduction, allowing higher larval abundances, while an environmentally unstable year could alter reproductive processes. Local topography influences environmental conditions: El Quisco is more exposed to regional upwelling, and showed higher abundances, species richness, and a predominance of benthic species. Abrupt weekly fluctuations in ichthyoplankton composition and abundance point out that fish larvae can quickly respond to short-term environmental variations.

The California Current System is described in its regional setting using two modern datasets. Argo provides a broadscale view of the entire eastern North Pacific Ocean for the period 2004–2010, and the High Resolution XBT Network includes transects from Honolulu to San Francisco (1991–2010) and to Los Angeles (2008– 2010). Together these datasets describe a California Current of 500–800 km width extending along the coast from 43°N to 23°N. The mean southward transport of the California Current is about 5 Sv off Central and Southern California, with about 2.5 Sv of northward flow on its inshore side. Interannual variations are 50% or more of the mean transports. The salinity minimum in the core of the California Current is supplied by the North Pacific Current and by freshwater from the northern continental shelf and modified by along-shore geostrophic and across-shore Ekman advection as well as eddy fluxes and air–sea exchange. The heat and freshwater content of the California Current vary in response to the fluctuating strength of the along-shore geostrophic flow. On its offshore side, the California Current is influenced by North Pacific Intermediate Waters at its deepest levels and by Eastern Subtropical Mode Waters on shallower density surfaces. In total, the sources of the California Current, its alongshore advection, and its strong interactions with the inshore upwelling region and the offshore gyre interior combine to make this a rich and diverse ecosystem. The present work reviews previous contributions to the regional oceanography, and uses the new datasets to paint a spatially and temporally more comprehensive description than was possible previously. Published by Elsevier Ltd.

RESUMEN. Se analiza la evolución de un evento de surgencia costera (16 al 20 de enero de 1986), frente a punta Curaumilla (33°06&amp;#x27;S), sobre la base de la distribución espacial y temporal de temperatura, salinidad, oxígeno disuelto, nutrientes (nitrato, fosfato y silicato), viento y ...

The mesoscale distributions of chlorophyll-a (Chl-a) and associated physical and chemical variables off the northern coast of Chile are described using quasi-synoptic data obtained during the austral winter (August–September) and spring (November–December) of 1993. Surface ...