Seasonal Upwelling Research Articles

Mapping the spatial and temporal variability of the upwelling systems of the Australian south-eastern coast using 14-year of MODIS data

Coastal upwelling is important for marine ecosystems and the economy, because of its elevated primary and secondary productivity and large potential for fish catch. This study developed a scale-independent and semi-automatic image processing technique to map the upwelling areas along the 4500 km south-eastern coast of Australia from 14-year monthly MODIS Sea Surface Temperature (SST) data. The results show that there is significant spatial variability in the mapped upwelling areas, month to month, season to season and year to year. There is also strong temporal (month to month, seasonal and inter-annual) variability of the upwelling characteristics in area of influence, SST anomaly, chlorophyll-a concentrations and upwelling speed. This study identifies two prominent upwelling systems, the NSW system along the coast of New South Wales and the WVIC/SA system along the coast of western Victoria and adjacent South Australia. The NSW coastal upwelling system occurs more or less continuously from austral spring to autumn. The WVIC/SA coastal upwelling system is a seasonal upwelling system occurring in the austral summer. The NSW coastal upwelling system has a stronger upwelling intensity than the WVIC/SA system, in terms of area of influence, SST anomaly, chlorophyll-a concentrations and upwelling speed. We believe that the NSW coastal upwelling system, especially the northern and central parts, is mainly driven by the East Australian Current (EAC) and its eddies; while, the WVIC/SA coastal upwelling is a typical wind-driven system. In addition, the results indicate that the El Nino Southern Oscillation (ENSO) events are likely to have a low-to-moderate impact on both the NSW and the WVIC/SA coastal upwelling systems. The El Nino (La Nina) events tend to strengthen (weaken) upwelling intensity.

Population Size and Breeding Phenology of Red-Billed Tropicbirds (Phaethon aethereus) on Iles de la Madeleine, Senegal

The breeding phenology and nest site distribution of Red-billed Tropicbirds (Phaethon aethereus) was monitored from 6 June 2014 to 18 May 2016 on Parc National des Iles de la Madeleine, Senegal. During this period, this study site was visited every 15 days to record active nests and their contents (eggs or chicks). We found up to 76 nest sites but only 49 were active in 2014-2015 and 45 in 2015-2016. Red-billed Tropicbirds bred throughout the year but numbers of active nests peaked from October to January, which may be related to the seasonality of ocean upwelling. Nests were aggregated in four areas and their distribution and occupancy may be related to the direction of the wind during the seasonal peak of reproduction from October to May. The breeding success was generally high (62.9% in 2014-2015 and 47.3% in 2015-2016) compared to other colonies breeding in less productive waters. Given the singularity and small size of this population, monitoring, management and strict protection is clearly needed to guarantee its viability.

Age interpretation in eulachon (Thaleichthys pacificus) as suggested by otolith microchemical signatures

Eulachon (Thaleichthys pacificus) are forage fish that play an important role in the ecosystem as prey for many species. Given their continuing population decline, determining accurate ages is necessary for age-structured stock assessments. This study employed microchemistry analysis to identify group differences and help interpret growth zone patterns on otolith surfaces. Specimens were collected off the coast of Oregon, in the coastal areas of Southeast Alaska, and in the southeastern Bering Sea. Laser-ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS) was used to measure elemental ratios in the otoliths along a continuous track from the core to the proximoventral margin. Ba:Ca, Sr:Ca, Zn:Ca, and Mg:Ca signatures suggested that eulachon specimens from three geographic regions are different based on their elemental profiles. For the Oregon specimens, fluctuations in Ba:Ca and Zn:Ca signatures appeared consistent with otolith growth zones and most likely were the result of seasonal coastal upwelling events. Variations in Ba:Ca and Zn:Ca were useful as annual markers for eulachon otoliths from the Bering Sea. For the Southeast Alaska specimens, analysis of the Ba:Ca and Zn:Ca oscillations was not straightforward. Further work is needed to understand the link between otolith microchemistry, fish physiology, and regional environmental factors.

Formulation of an Empirical Relation between Chlorophyll and Sea Surface Temperature in the Southeastern Arabian Sea

Present study formulates an empirical relation between sea surface temperature (SST) and chlorophyll (Chl) in the Southeastern Arabian Sea using data collected during 2017. SST was found to decrease due to upwelling of cold nutrient rich waters, thus causing enhancement of Chl in the coastal and nearshore waters. Based on this, an empirical relationship exists which is inversely correlated during peak upwelling and intense biological production. The linear regression generated a significant correlation coefficient (0.52 ≤ R2 ≥ 0.64) in the month of July, August and October. Although other factors influence Chl, SST can be considered as a significant indicator of biological production with respect to seasonal upwelling. Among the empirical relations, a definite single equation requires the assessment of subsurface Chl to reveal the underlying relationship.

Dynamic of ENSO towards upwelling and thermal front zone in the east coast of Peninsular Malaysia

The El Nino Southern Oscillation (ENSO) is a natural phenomenon that relates to the fluctuation of temperatures over the Pacific Ocean. The ENSO significantly affects the ocean dynamics including upwelling event and coastal front. A recent study discovered the seasonal upwelling in the east coast of Peninsular Malaysia (ECPM), which is significant to the fishery industry in this region. Thus, it is vital to have a better understanding of the influence of ENSO towards the coastal upwelling and thermal front in the ECPM. The sea surface temperature (SST) data achieved from moderate resolution imaging spectroradiometer (MODIS) aboard Aqua satellite are used in this study to observe the SST changes from 2005 to 2015. However, due to cloud cover issue, a reconstruction of data set is applied to MODIS data using the data interpolating empirical orthogonal function (DINEOF) to fill in the missing gap in the dataset based on spatial and temporal available data. Besides, a wavelet transformation analysis is done to determine the temperature fluctuation throughout the time series. The DINEOF results show the coastal upwelling in the ECPM develops in July and reaches its peak in August with a clear cold water patch off the coast. There is also a significant change of SST distribution during the El Nino years which weaken the coastal upwelling event along the ECPM. The wavelet transformation analysis shows the highest temperature fluctuation is in 2009–2010 which indicates the strongest El Nino throughout the time period. It is suggested that the El Nino is favourable for the stratification in water column thus it is weakening the upwelling and thermal frontal zone formation in ECPM waters.

Spatial and temporal distribution of mobulid ray species in the eastern Pacific Ocean ascertained from observer data from the tropical tuna purse-seine fishery

This research focuses on the description of the spatial and temporal distributions of mobulid ray species (Mobula birostris, Mobula mobular, Mobula thurstoni, Mobula tarapacana and Mobula munkiana) using data from the observer program (1993–2014) of the Inter-American Tropical Tuna Commission (IATTC). The tuna purse seine operations in the region extend from 70 to 150°W to 20°S-30°N. Significant differences on the captures per sets between fishing modes and species were found. Results showed that the most common species taken are M. thurstoni, M. mobular and M. birostris in School sets (sets on unassociated tuna schools). The temporal distributions showed high variability of the catches by species and years. The spatial distribution showed several areas of importance depending of the type of fishing, such as the coast of Peru, Galagapos or the Costa Rica Dome, and possible relationships with some oceanographic processes of the eastern Pacific Ocean (i.e. coastal and seasonal upwelling systems). The frequency of the captures per set showed that, although the greatest numbers caught in a set were very low (around 53.7% of sets with one capture), in some areas and periods there were captures of aggregates of hundreds of individuals of some of these species, such as Galapagos Islands during December, Costa Rica Dome during August, or Baja California during June. These events are of biological interest, and may offer good opportunities for conservation. This project has been developed with the aim of identifying the most important areas for these bycatch species and thus, improving the knowledge on them to reduce their mortality.

Dinoflagellate cyst production in the Cariaco Basin: A 12.5 year-long sediment trap study

Seasonal and interannual variability in dinoflagellate cyst production were assessed using a 12.5 year-long sediment trap time series from the Cariaco Basin (southern Caribbean Sea). This study constitutes the longest such time series published to date, providing robust patterns of variability for individual dinoflagellate cyst taxa as well as for major phytoplanktonic and (micro-)zooplanktonic groups at the site. Cyst production is interpreted in the context of physico-chemical properties measured in situ at the mooring site (primarily reflecting seasonal upwelling), and considering potential interactions with other major components of the pelagic food web (e.g., diatoms, ciliates, copepods).The time series consists in >300 sediment trap samples, each representing ∼14 days of sedimentation, collected at the CARIACO station between Nov. 8, 1996 and May 19, 2009. Mass fluxes of biogenic silica, calcium carbonate and organic carbon reflect dominantly the timing and strength of wind-driven, seasonal upwelling that brings colder, nutrient-rich waters to the surface, fostering primary productivity and the export of biogenous materials to the depths. On seasonal time scales, dinoflagellate cyst production is closely coupled with upwelling strength, with higher cyst fluxes consistently observed under active upwelling conditions (average of 50.5 × 103 cysts m−2 day−1) compared to non-active upwelling intervals (29.0 × 103 cysts m−2 day−1). Year-to-year variability is characterized by a large increase in cyst production observed over the last ∼4 years of the time series (2006–2009) and minimum cyst fluxes recorded in the years 1998 and 1999, following the strong 1997/98 El Niño event.Dinoflagellate cyst assemblages are dominated by Brigantedinium spp. (59.1%), accompanied by Echinidinium delicatum (10.8%), Bitectatodinium spongium (8.4%), Spiny brown type A (2.9%) and Echinidinium spp. (2.4%). Cyst produced by both autotrophic and heterotrophic dinoflagellates generally respond positively to upwelling in the basin. Most cyst taxa are associated with active upwelling conditions (e.g., Bitectatodinium spongium, Brigantedinium spp., Echinidinium delicatum, Quinquecuspis concreta, Selenopemphix quanta, Spiny brown type C), with some showing higher fluxes under active but weak upwelling conditions (e.g., Echinidinium granulatum, Echinidinium spp., cyst of P. fukuyoi, Spiny brown type A). Other cyst taxa tend to show higher abundances at the onset of upwelling conditions (e.g., Echinidinium aculeatum, cyst of Protoperidinium stellatum) or following active upwelling intervals (e.g., Lejeunecysta marieae, Selenopemphix nephroides). The detailed response of each dinoflagellate cyst taxon to environmental variability is presented in the form of an atlas, providing photomicrographs and detailing overall monthly production, contribution to the total trap assemblage as well as cyst production over the 12.5 years of the time series.

Small copepods could channel missing carbon through metazoan predation.

Global ecosystem models are essential tools for predicting climate change impacts on marine systems. Modeled biogenic carbon fluxes in the ocean often match measured data poorly and part of this could be because small copepods (<2 mm) are modeled as unicellular feeders grazing on phytoplankton and microzooplankton. The most abundant copepods from a seasonal upwelling region of the Eastern North Atlantic were sorted, and a molecular method was applied to copepod gut contents to evaluate the extent of metazoan predation under two oceanographic conditions, a trophic pathway not accounted for in global models. Scaling up the results obtained herein, based on published field and laboratory estimates, suggests that small copepods could ingest 1.79–27.20 gigatons C/year globally. This ignored metazoan‐copepod link could increase current estimates of biogeochemical fluxes (remineralization, respiration, and the biological pump) and export to higher trophic levels by 15.6%–24.4%. It could also account for global discrepancies between measured daily ingestion and copepod metabolic demand/growth. The inclusion of metazoan predation into global models could provide a more realistic role of the copepods in the ocean and if these preliminary data hold true at larger sample sizes and scales, the implications would be substantial at the global scale.

Seasonal succession of tropical community structure, abundance, and biomass of five zooplankton taxa in the central Mexican Pacific

The seasonal succession of species community structure, abundance and carbon biomass of five zooplankton taxa (Copepoda, Euphausiacea, Chaetognatha, Amphipoda and fish larvae) and their variability during different oceanographic conditions was investigated on the continental shelf of the central Mexican Pacific (19°N, 105°W) during a monthly time-series (1996–1998). These zooplanktonic taxa included 291 species, with maximum species richness during El Niño 1997–98, when 54 tropical oceanic species invaded the continental shelf. This typical offshore community was advected onshore by the anomalous intrusion of Subsurface Equatorial water mass which caused + 7 °C temperature anomalies. Nineteen species comprised the bulk of the abundance (91%) and biomass (87%) of the five zooplankton taxa. Multivariate statistical analysis revealed four species assemblages associated with distinct oceanographic conditions: (1) mixed water column period (upwelling; February–June, non-El Niño period) characterized by high abundance and carbon biomass of omnivorous zooplankters (copepods Subeucalanus subcrassus, Centropages furcatus, Canthocalanus pauper, Temora discaudata, and Subeucalanus subtenuis, euphausiid Euphausia distinguenda, and fish larvae Bregmaceros bathymaster); (2) stratified water column period (July–January, non-El Niño period) with low-moderate abundance and biomass of the predominant species of the first group plus the euphausiid E. lamelligera, the chaetognaths Flaccisagitta enflata and Zonosagitta bedoti, and the tropical amphipod Hyperioides sibaginis; and (3 and 4) two highly diverse assemblages associated with El Niño-stratified conditions and post El Niño (July 1997–December 1998). These last two assemblages were distinguished by a high numerical dominance of carnivores (F. enflata, Z. bedoti, and H. sibaginis) and a pronounced decline of abundances of omnivore copepods, euphausiids, and fish larvae. Both the seasonal upwelling dynamics and the interannual-scale El Niño events shaped the tropical zooplankton community structure succession of this neritic ecosystem. The local community structure modulates the function and productivity of this ecosystem, which sustains regional fisheries and ecotouristic activities. More frequent, intense or even longer El Niño events may significantly decrease zooplanktonic carbon biomass and trophic transfer through the neritic epipelagic food web, resulting in impoverishment of the shelf biota with negative economic implications.

Denitrification rates of culturable bacteria from a coastal location turning temporally hypoxic

Abstract Nitrate reduction plays a key role in the biogeochemical dynamics and microbial ecology of coastal upwelling systems. Seasonal upwelling in the eastern Arabian Sea entrains nitrate rich waters to the surface, the intense productivity that follows leads to oxygen depletion and then denitrification. Heterotrophic bacteria comprise diverse functional groups. Both aerobic and facultative anaerobic heterotrophic bacteria capable of nitrate reduction are important functional groups in the nitrogen cycle due to their ability to respire anaerobically using nitrogen oxides as electron acceptors, which are reduced to nitrous oxide and dinitrogen. However little is known from the coastal Arabian Sea on the types/species of culturable bacteria catalyzing this crucial step. To recognize the species composition of the culturable fractions involved in nitrate reduction and nitrous oxide production, as many as 360 cultures of native heterotrophic bacteria were isolated and screened for nitrate reduction. Isolates were identified by sequencing their 16S rRNA gene and the rate of nitrate reduction and production of nitrous oxide by representatives of 30 different species of bacteria were measured. Close to 77% (or 277 of 360) of the cultures were found to be nitrate reducers, which grouped into 30 different species. Further, the nitrate reduction rates and nitrous oxide production by these 30 representative nitrate reducing species were measured. Cultures were capable of nitrate reduction up to 2.40 (×10−14) mol cell−1 and 5.54 (×10−15) mol cell−1 of nitrous oxide. This high fraction of culturable bacteria reducing nitrate and producing N2O in low oxygen conditions ought to reflect their important role in biogeochemical processes in the tropical coastal water experiencing hypoxia during SuM (Summer monsoon) and FIM (Fall intermonsoon) in the monsoon affected regions.

Estudios de zooplancton marino en Costa Rica: una revisión y perspectivas a futuro

This review summarizes marine zooplankton research performed in the Costa Rican Pacific and Caribbean coasts and at Isla del Coco National Park. Composition, abundance, biomass, distribution and some ecological features of the zooplankton for each system is discussed. Pacific coastal zooplankton composition has been described in Bahía Salinas and Bahía Culebra. The local oceanography of these bays is heavily influenced by the Papagayo wind jet, which produces seasonal coastal upwelling and most likely drives the seasonal changes in zooplankton abundance and biomass. Copepods and ostracods were the dominant taxonomic groups throughout the year with a strong seasonality, furthermore 53 hydromedusae species has been found, where Liriope tetraphylla (Chamisso &amp; Eysenhardt, 1821), Solmundella bitentaculata (Quoy &amp; Gaimard, 1833) and Aglaura hemistoma (Péron &amp; Lesueur, 1810), were the most abundant species. Zooplankton herbivory rates at Gulf of Nicoya estuary was estimated over 50 % removal of primary production. This is a typical value for tropical productive environments. Copepods numerically dominated zooplankton community from the Gulf of Nicoya. Other dominant taxa includes merozooplanktonic decapod larvae and ichthyoplankton. Biomass is high and there are strong crossshelf gradients in the Gulf. Zooplankton collected in the southern Pacific coast (close to Isla del Caño) is also dominated by copepods, while Bahía Coronado has a mixed zooplankton composition of oceanic and coastal transition waters. In Golfo Dulce, zooplankton is highly diverse and dominated by copepods, appendicularians, and ostracods. About 35 % of daily primary production is consumed by microzooplankton, and zooplankton adapt to anomalous conditions of El Niño-Southern Oscillation (ENSO). Coco´s Island, and other oceanic islands in the Eastern Tropical Pacific are “hot spot” of zooplankton diversity, where &gt; 160 zooplankton species have been reported (predominantly copepods). The biomass is dominated by mesozooplankton, and new species records for the Eastern Tropical Pacific have been found in this insular ecosystem. In the other hand, early works of 1980 carried out at Caribbean coast (Cahuita National Park), show a considerably low zooplankton diversity and abundance while research at the end of the 2000 decade recognized a significant increase in zooplankton diversity, specially fish larvae. Recent zooplankton studies have added six new copepod species and several new records of species from different taxonomic groups such as appendicularians, amphipods, chaetognats, euphausiids, gastropods, and polychaetes. Future work should focus on monthly long-term monitoring programs to investigate the effects of ocean acidification and the trophic dynamics associated with fisheries. Alike, longterm studies are needed to see trends of change in planktonic communities, especially comparing areas under human activity in the coastal zone (tourism, port, urban development) with protected areas as targets for study. An increase of sampling efforts must be done in the relatively understudied Northern Caribbean coast.

Late Holocene palaeotemperatures and palaeoenvironments in the Southeastern Brazilian coast inferred from otolith geochemistry

Holocene palaeoceanography and climatic reconstructions were evaluated based on proxy analyses of fish otoliths from shellmounds located along the coast of Rio de Janeiro State, Brazil. Modern coastal seasonal upwelling is associated with the ascension of a deep and cold-water mass as a consequence of persistent NE winds that affect the climate in southeastern Brazil. However, this seasonal influence and the effect of the Holocene palaeoenvironment on shallow water are poorly known. In this work, coastal palaeotemperatures were estimated based on the geochemical analyses of otolith. The results of the δ18O and δ13C analyses from Holocene otoliths, obtained from coastal shellmounds separated by a distance of almost 200 km, show two distinctive otolith-derived palaeotemperature signals in a coastal region under upwelling influence. Additionally, this analysis suggests that the fish lived in marine waters, showing similar microchemistry values composition when compared with modern marine otoliths.

Physico-chemical and biological factors influencing dinoflagellate cyst production in the Cariaco Basin

Abstract. We present a 2.5-year-long sediment trap record of dinoflagellate cyst production in the Cariaco Basin, off Venezuela (southern Caribbean Sea). The site lies under the influence of wind-driven, seasonal upwelling which promotes high levels of primary productivity during boreal winter and spring. Changes in dinoflagellate cyst production is documented between November 1996 and May 1999 at ∼ 14-day intervals and interpreted in the context of in situ observations of physico-chemical and biological parameters measured at the mooring site. Dinoflagellate cyst assemblages are diverse (57 taxa) and dominated by cyst taxa of heterotrophic affinity, primarily Brigantedinium spp. (51 % of the total trap assemblage). Average cyst fluxes to the trap are high (17.1 × 103 cysts m−2 day−1) and show great seasonal and interannual variability. On seasonal timescales, dinoflagellate cyst production responds closely to variations in upwelling strength, with increases in cyst fluxes of several protoperidinioid taxa observed during active upwelling intervals, predominantly Brigantedinium spp. Cyst taxa produced by autotrophic dinoflagellates, in particular Bitectatodinium spongium, also respond positively to upwelling. Several spiny brown cysts contribute substantially to the assemblages, including Echinidinium delicatum (9.7 %) and Echinidinium granulatum (7.3 %), and show a closer affinity to weaker upwelling conditions. The strong El Niño event of 1997/98 appears to have negatively impacted cyst production in the basin with a 1-year lag, and may have contributed to the unusually high fluxes of cysts type Cp (possibly the cysts of the toxic dinoflagellate Cochlodinium polykrikoides sensu Li et al., 2015), with cyst type Cp fluxes up to 11.8 × 103 cysts m−2 day−1 observed during the weak upwelling event of February–May 1999. Possible trophic interactions between dinoflagellates and other major planktonic groups are also investigated by comparing the timing and magnitude of cyst production with proxies for phytoplanktonic communities (from photopigment data) and micro- to macrozooplankton abundance indicators (from palynological data) at the site. This work provides new, detailed insights into the ecology of cyst-producing dinoflagellates and will allow for more detailed interpretations of fossil assemblages extracted from sedimentary records in the basin and elsewhere.

Natural ocean acidification at Papagayo upwelling system (north Pacific Costa Rica): implications for reef development

Abstract. Numerous experiments have shown that ocean acidification impedes coral calcification, but knowledge about in situ reef ecosystem response to ocean acidification is still scarce. Bahía Culebra, situated at the northern Pacific coast of Costa Rica, is a location naturally exposed to acidic conditions due to the Papagayo seasonal upwelling. We measured pH and pCO2 in situ during two non-upwelling seasons (June 2012, May–June 2013), with a high temporal resolution of every 15 and 30 min, respectively, using two Submersible Autonomous Moored Instruments (SAMI-pH, SAMI-CO2). These results were compared with published data from the 2009 upwelling season. Findings revealed that the carbonate system in Bahía Culebra shows a high temporal variability. Incoming offshore waters drive intra- and interseasonal changes. Lowest pH (7.8) and highest pCO2 (658.3 µatm) values measured during a cold-water intrusion event in the non-upwelling season were similar to those minimum values reported from upwelling season (pH = 7.8, pCO2 = 643.5 µatm), unveiling that natural acidification also occurs sporadically in the non-upwelling season. This affects the interaction of photosynthesis, respiration, calcification and carbonate dissolution and the resulting diel cycle of pH and pCO2 in the reefs of Bahía Culebra. During the non-upwelling season, the aragonite saturation state (Ωa) rises to values of &gt; 3.3 and during the upwelling season falls below 2.5. The Ωa threshold values for coral growth were derived from the correlation between measured Ωa and coral linear extension rates which were obtained from the literature and suggest that future ocean acidification will threaten the continued growth of reefs in Bahía Culebra. These data contribute to building a better understanding of the carbonate system dynamics and coral reefs' key response (e.g., coral growth) to natural low-pH conditions, in upwelling areas in the eastern tropical Pacific and beyond.

Seasonal differences in egg size in three species of crabs from a tropical upwelling zone

ABSTRACTEgg size and offspring size are fundamentally important aspects of the life histories of all animals. However the impact of environmental conditions on intraspecific variation in egg size of marine invertebrates is poorly documented. Here we followed three species of intertidal crabs Xanthodius sternberghii, Petrolisthes armatus and Clibanarius albidigitus to understand how seasonal environmental variation in temperature and salinity associated with seasonal upwelling impacts egg size. Ovigerous females of both P. armatus and C. albidigitus were found year round, while X. sternberghii has a limited reproductive season, with ovigerous females found only between November and February. In all three species more than half of the variation in egg size was attributable to variation among broods from different females. Eggs collected during the dry, upwelling season were significantly larger than those collected during the wet, non-upwelling season. Multiple regression analysis showed that average egg size from each brood was significantly negatively correlated with temperature for all three species. Egg size was also negatively correlated with salinity in P. armatus when we controlled for temperature. Overall these results support the idea that changes in environmental temperature caused by seasonal upwelling play a significant role in generating seasonal differences in egg size.

Observations of Seasonal Upwelling and Downwelling in the Beaufort Sea Mediated by Sea Ice

AbstractWe present observational estimates of Ekman pumping in the Beaufort Gyre region. Averaged over the Canada Basin, the results show a 2003–14 average of 2.3 m yr−1 downward with strong seasonal and interannual variability superimposed: monthly and yearly means range from 30 m yr−1 downward to 10 m yr−1 upward. A clear, seasonal cycle is evident with intense downwelling in autumn and upwelling during the winter months, despite the wind forcing being downwelling favorable year-round. Wintertime upwelling is associated with friction between the large-scale Beaufort Gyre ocean circulation and the surface ice pack and contrasts with previous estimates of yearlong downwelling; as a consequence, the yearly cumulative Ekman pumping over the gyre is significantly reduced. The spatial distribution of Ekman pumping is also modified, with the Beaufort Gyre region showing alternating, moderate upwelling and downwelling, while a more intense, yearlong downwelling averaging 18 m yr−1 is identified in the northern Chukchi Sea region. Implications of the results for understanding Arctic Ocean dynamics and change are discussed.

Oxygen modulates bacterial community composition in the coastal upwelling waters off central Chile

Bacterial community composition and its relationship to oxygen were investigated in the non-sulfidic shelf waters exposed to seasonal upwelling and oxygen deficiency off central Chile. Using 16S rRNA gene clone libraries, terminal restriction fragment length polymorphism (T-RFLP) and iTAG sequencing analyses of nearly 4 years of monthly sampling through the water column (5–80 m depth), we found a clear partitioning of community composition that could be attributed to dissolved oxygen (Spearman correlation coefficient = 0.578) in comparison to other environmental variables, such as light, fluorescence, temperature, salinity, microbial abundance or nutrients. Bacteroidetes (orders Sphingobacteriales and Flavobacteriales), SAR11 (subclades Ia - Candidatus Pelagibacter ubique and II), an unclassified group of Alphaproteobacteria, and SAR86 dominated in waters containing dissolved oxygen concentrations ≥70 μM. In contrast, taxonomic groups associated with capabilities of either oxidative or reductive cycling of inorganic sulfur dominated in waters with dissolved oxygen from ~70 μM to undetectable levels. The dominant groups were Arctic96BD-19, SUP05 and SAR324 (sulfur oxidation) and Desulfobacterales (sulfate reduction). Desulfobacterales are known to come primarily from sulfidic, nitrate/nitrite-depleted waters and sediments. Their presence, therefore, provides taxonomic evidence for pelagic dissimilatory sulfate reduction within oxygen-depleted coastal environments.

Response of O&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; and pH to ENSO in the California Current System in a high-resolution global climate model

Abstract. Coastal upwelling systems, such as the California Current System (CalCS), naturally experience a wide range of O2 concentrations and pH values due to the seasonality of upwelling. Nonetheless, changes in the El Niño–Southern Oscillation (ENSO) have been shown to measurably affect the biogeochemical and physical properties of coastal upwelling regions. In this study, we use a novel, high-resolution global climate model (GFDL-ESM2.6) to investigate the influence of warm and cold ENSO events on variations in the O2 concentration and the pH of the CalCS coastal waters. An assessment of the CalCS response to six El Niño and seven La Niña events in ESM2.6 reveals significant variations in the response between events. However, these variations overlay a consistent physical and biogeochemical (O2 and pH) response in the composite mean. Focusing on the mean response, our results demonstrate that O2 and pH are affected rather differently in the euphotic zone above ∼ 100 m. The strongest O2 response reaches up to several hundreds of kilometers offshore, whereas the pH signal occurs only within a ∼ 100 km wide band along the coast. By splitting the changes in O2 and pH into individual physical and biogeochemical components that are affected by ENSO variability, we found that O2 variability in the surface ocean is primarily driven by changes in surface temperature that affect the O2 solubility. In contrast, surface pH changes are predominantly driven by changes in dissolved inorganic carbon (DIC), which in turn is affected by upwelling, explaining the confined nature of the pH signal close to the coast. Below ∼ 100 m, we find conditions with anomalously low O2 and pH, and by extension also anomalously low aragonite saturation, during La Niña. This result is consistent with findings from previous studies and highlights the stress that the CalCS ecosystem could periodically undergo in addition to impacts due to climate change.

Coastal upwelling seasonality and variability of temperature and chlorophyll in a small coastal embayment

While the seasonality of wind-driven coastal upwelling in eastern boundary upwelling systems has long been established, many studies describe two distinct seasons (upwelling and non-upwelling), a generalized framework that does not capture details relevant to marine ecosystems. In this contribution, we present a more detailed description of the annual cycle and upwelling seasonality for an understudied location along the central California coast. Using both the mean monthly upwelling favorable wind stress and the monthly standard deviation, we define the following seasons (contiguous months) and a transitional period (non-contiguous months): “Winter Storms” season (Dec-Jan-Feb), “Upwelling Transition” period (Mar and Jun), “Peak Upwelling” season (Apr-May), “Upwelling Relaxation” season (Jul-Aug-Sep), and “Winter Transition” season (Oct-Nov). In order to describe the oceanic response to this upwelling wind seasonality, we take advantage of nearly a decade of full water-column measurements of temperature and chlorophyll made using an automated profiling system at the end of the California Polytechnic State University Pier in San Luis Obispo Bay, a small (~ 2km wide near study site) and shallow (~ 10m average bay depth) coastal embayment. Variability and average-year patterns are described inside the bay during the various upwelling seasons. Moreover, the role of the local coastline orientation and topography on bay dynamics is also assessed using long-term measurements collected outside of the bay. The formation of a seasonally variable upwelling shadow system and potential nearshore retention zone is discussed. The observations presented provide a framework on which to study interannual changes to the average-year seasonal cycle, assess the contribution of higher-frequency features to nearshore variability, and better predict dynamically and ecologically important events.

The Effect of Alongcoast Advection on Pacific Northwest Shelf and Slope Water Properties in Relation to Upwelling Variability.

The Northern California Current System experiences highly variable seasonal upwelling in addition to larger basin‐scale variability, both of which can significantly affect its water chemistry. Salinity and temperature fields from a 7 year ROMS hindcast model of this region (43°N–50°N), along with extensive particle tracking, were used to study interannual variability in water properties over both the upper slope and the midshelf bottom. Variation in slope water properties was an order of magnitude smaller than on the shelf. Furthermore, the primary relationship between temperature and salinity anomalies in midshelf bottom water consisted of variation in density (cold/salty versus warm/fresh), nearly orthogonal to the anomalies along density levels (cold/fresh versus warm/salty) observed on the upper slope. These midshelf anomalies were well‐explained (R 2 = 0.6) by the combination of interannual variability in local and remote alongshore wind stress, and depth of the California Undercurrent (CUC) core. Lagrangian analysis of upper slope and midshelf bottom water shows that both are affected simultaneously by large‐scale alongcoast advection of water through the northern and southern boundaries. The amplitude of anomalies in bottom oxygen and dissolved inorganic carbon (DIC) on the shelf associated with upwelling variability are larger than those associated with typical variation in alongcoast advection, and are comparable to observed anomalies in this region. However, a large northern intrusion event in 2004 illustrates that particular, large‐scale alongcoast advection anomalies can be just as effective as upwelling variability in changing shelf water properties on the interannual scale.