Coastal Upwelling Conditions Research Articles

The 2019 Brazilian oil spill: Insights on the physics behind the drift

This study uses global numerical model results of ocean and atmospheric circulation, as well as local wind, wave and current meter data, to investigate the structure of the ocean and coastal circulation potentially associated with the transport of oil that affected thousands of kilometers of the Brazilian coast in 2019. Our analysis suggests the oil was brought close to the continental shelf sometime in August 2019 by the southern branch of South Equatorial Current, and was initially advected towards the north by the North Brazilian Current and shelf currents pushed by SE winds. The onset of negative along-shore winds close to the coast in September–October 2019 turned the coastal along-shore drift south, a situation that persisted throughout the spring and summer seasons. Along the east coast, where observational data was available, landward cross-shelf flows below 17 m of depth, associated with coastal upwelling conditions, advected the oil from the slope onto the outer and mid-shelf. On the inner-shelf the oil was finally pushed towards the beaches by the wave action close to the bottom. Reports of oil arriving on the east coast followed changes in coastal wind and current patterns very closely. It is suggested that before reaching the shelf, the oil drifted at depths larger than 17 m, perhaps reaching several tens of meters.

Cross-shelf distribution of decapod larvae in a coastal upwelling zone of northern Chile: some oceanographic implications

The northern of Chile is one of the most productive and permanent upwelling systems of the large Humboldt Current System. However, do not investigations have been developed about the decapod larvae dynamics in this region, characterized by its narrow continental shelf and an oxygen minimal zone (OMZ) very shallow (<50 m). Four oceanographic campaigns carried out in a coastal upwelling zone off northern Chile in 2003 were used to analyze the dispersal patterns of 15 taxa from decapods larvae selected. The coastal upwelling conditions showed a maximum Ekman transport value (Mx) in January and a minimum in May, while the temperature and salinity characteristics defined four types of waters named a) cold upwelling waters (UW), b) warm trapped waters (WTW), c) upwelling front waters (UFW) and d) oceanic front waters (OFW), which showed different concentrations of dissolved oxygen, OMZ depth (<1 mL L−1) and chlorophyll-a concentrations, respectively. Decapod larvae with the highest abundance and frequency were Cancer spp., Emerita analoga, Pinnaxodes chilensis, Callianassidae sp., Pagurus sp. and Allopetrolisthes sp., from adults of diverse habitats, characterized by different development stages and periods. The offshore weighted distance (Ğ) estimated for the decapod larvae allowed the differentiation of three main groups. a) group formed by high dispersion larvae (>11 km), with five zoea stages and associated to the UFW waters, b) group formed by mean dispersion larvae (between 5 and 8 km) and distributed in upwelling waters (UW), and c) group showing lower horizontal dispersions (<4 km), which significantly and negatively correlated to the OMZ in UW and WTW-type waters. The different cross-shelf distribution patterns relative to the oceanographic conditions were compared with other upwelling system, and larval behavior, morphology, environmental requirements and development period of different decapods were discussed.

Effects of current and future coastal upwelling conditions on the fertilization success of the red abalone (Haliotis rufescens)

Acidification, deoxygenation, and warming are escalating changes in coastal waters throughout the world ocean, with potentially severe consequences for marine life and ocean-based economies. To examine the influence of these oceanographic changes on a key biological process, we measured the effects of current and expected future conditions in the California Current Large Marine Ecosystem on the fertilization success of the red abalone (Haliotis rufescens). Laboratory experiments were used to assess abalone fertilization success during simultaneous exposure to various levels of seawater pH (gradient from 7.95 to 7.2), dissolved oxygen (DO) (∼60 and 180 µm.kg SW) and temperature (9, 13, and 18 °C). Fertilization success declined continuously with decreasing pH but dropped precipitously below a threshold near pH 7.55 in cool (9 °C—upwelling) to average (13 °C) seawater temperatures. Variation in DO had a negligible effect on fertilization. In contrast, warmer waters (18 °C) often associated with El Niño Southern Oscillation conditions in central California acted antagonistically with decreasing pH, largely reducing the strong negative influence below the pH threshold. Experimental approaches that examine the interactive effects of multiple environmental drivers and also strive to characterize the functional response of organisms along gradients in environmental change are becoming increasingly important in advancing our understanding of the real-world consequences of changing ocean conditions.

Mineral and elemental indicators of post-glacial changes in sediment delivery and deposition under a western boundary upwelling system (Cabo Frio, southeastern Brazil)

Minerals and elements are important proxies that can provide information about variations in the delivery and deposition of coastal ocean sediments associated with past climate changes. In this study, postglacial changes in the accumulation of sediments on the upper shelf of southeastern Brazil are linked to the evolution of regional paleoceanographic and continental paleoclimatic conditions during the last 14.4kyr CAL BP. Mineralogical and major and trace element analyses of a 14C-dated sediment core identify three main lithostratigraphic units of this core that reveal a succession of changes in sediment delivery and accumulation as postglacial sea level rose and Holocene climate on land evolved. The depositional setting has transitioned in response to the large sea level rise prior to 9.9kyr CAL BP from being a shallow water high energy environment to a deeper water one. This location has since then been a lower energy environment that has persisted into modern times. Due to the high marine productivity associated with the Cabo Frio upwelling system in an oxygenated water column, the sediments have shown a complex and dynamic redox condition, making variations in redox-sensitive trace elements indicative of changes in primary production and organic matter diagenesis at this location. After sea level stabilized ~9kyr CAL BP, variations in fluxes of Al, Fe, Ca, and minerals were small, indicating that climate driven changes had only secondary controls on delivery of detrital sediment components to the Cabo Frio shelf. Modern coastal upwelling conditions and the onset of mid-shelf organic-rich sediment deposition were established after 9.9CAL kyr BP.

The structure of planktonic communities under variable coastal upwelling conditions off Cape Ghir (31°N) in the Canary Current System (NW Africa)

Cape Ghir (∼31°N), in the Canary Current System, is an area of permanent coastal upwelling with maximum intensity in summer–autumn, when a strong across-shore thermal gradient and increased mesoscale activity are present. The effects of spatial (cross-shore transect with 7 stations) and temporal (5 dates: from December 2008 to October 2009) variations in upwelling conditions on the structure of planktonic communities (functional groups, size and taxa composition, abundance and carbon biomass) were investigated. Multivariate analysis of the environmental variables enabled both spatial separation of the stations, based primarily on differences in nutrient concentration, and a temporal distinction of upwelling phases, based mostly on differences in sea surface temperature and number of days favourable to upwelling. These clusters were also representative of the time–space variability in the planktonic communities, suggesting that upwelling conditions directly influence their structure. For most of the cruises, the microplankton (mainly diatoms and auto/mixotrophic dinoflagellates) made the highest contributions to photoautotrophic carbon (C) biomass but the nanoplankton (mainly flagellates and dinoflagellates) made the largest contributions to total chlorophyll-a (Chl-a). Mean heterotrophic:autotrophic biomass ratios (from pico-to microplankton during three cruises) were mostly ⩽1 (normal pyramid), as expected for productive coastal areas, only when the contribution of mixotrophy was considered. A mixed composition of functional groups of autotrophs/mixotrophs in the coastal and coastal transition zones off C. Ghir is probably the result of the nutrient contents in the upwelled waters since potential silicate or nitrate limitation together with a relatively high C:Chl-a in the micro-phytoplankton were detected during some of the cruises. Temporal changes in diatom taxa with different nutrient requirements also suggested a strong influence of nutrients. The comparatively lower nutrient contents in the upwelled waters off Cape Ghir are linked to the regional circulation patterns, a relatively narrow shelf (lower residence time of the upwelled waters), a higher level of mesoscale activity, and with weak to moderate wind intensities for most part of the year.

Marine radiocarbon reservoir age variation in Donax obesulus shells from northern Peru: Late Holocene evidence for extended El Nino

For at least 6 m.y., El Nino events have posed the greatest environmental risk on the Peruvian coast. A better understanding of El Nino is essential for predicting future risk and growth in this tropical desert. To achieve this we analyzed archaeological and modern pre-bomb shells from the surf clam Donax for the radiocarbon reservoir effect (ΔR) to characterize late Holocene coastal upwelling conditions in northern Peru (8°14′S). Mean ΔR values from these shells suggest that modern upwelling conditions in this region were likely established between A.D. 539 and A.D. 1578. Our radiocarbon data suggest that upwelling conditions ca. A.D. 539 were less intense than those in modern times. The observed coastal water enrichment in 14 C may be consequence of frequent strong El Nino events or extended El Nino–like conditions. These ΔR-inferred marine conditions are in agreement with proposed extended El Nino activity in proxy and archaeological records of ca. A.D. 475–530. Extended El Nino conditions have been linked to political destabilization, societal transformation, and collapse of the Moche civilization in northern Peru. A return to such conditions would have significant impacts on the dense population of this region today and in the near future.

Shallow-marine sediment cores record climate variability and earthquake activity off Lisbon (Portugal) for the last 2000 years

Sea Surface Temperature (SST), river discharge and biological productivity have been reconstructed from a multi-proxy study of a high-temporal-resolution sedimentary sequence recovered from the Tagus deposition center off Lisbon (Portugal) for the last 2000 years. SST shows 2 °C variability on a century scale that allows the identification of the Medieval Warm Period (MWP) and the Little Ice Age (LIA). High Iron (Fe) and fine-sediment deposition accompanied by high n -alkane concentrations and presence of freshwater diatoms during the LIA (1300–1900 AD) (Science 292 (2001) 662) suggest augmented river discharge, whereas higher total-alkenone concentrations point to increased river-induced productivity. During the MWP (550–1300 AD) (Science 292 (2001) 662) larger mean-grain size and low values of magnetic susceptibility, and concentrations of Fe, n -alkanes, and n -alcohols are interpreted to reflect decreased runoff. At the same time, increased benthic and planktonic foraminifera abundances and presence of upwelling related diatoms point to increased oceanic productivity. On the basis of the excellent match found between the negative phases of the North Atlantic Oscillation (NAO) index and the intensified Tagus River discharge observed for the last century, it is hypothesized that the increased influx of terrigenous material during the LIA reflects a negative NAO-like state or the occurrence of frequent extreme NAO minima. During the milder few centuries of the MWP, stronger coastal upwelling conditions are attributed to a persistent, positive NAO-like state or the frequent occurrence of extreme NAO maxima. The peak in magnetic susceptibility, centered at 90 cm composite core depth (ccd), is interpreted as the result of the well-known 1755 AD Lisbon earthquake. The Lisbon earthquake and accompanying tsunami are estimated to have caused the loss of 39 cm of sediment (355 years of record—most of the LIA) and the instantaneous deposition of a 19-cm sediment bed.

Relationships between Coastal Ocean Conditions and Survival Rates of Northeast Pacific Salmon at Multiple Lags

AbstractWe tested the hypothesis that survival rates from spawners to recruits in Pacific salmon Oncorhynchus spp. are primarily related to coastal ocean conditions during migration to the sea and soon after. We correlated measures of survival rate in units of loge(recruits/spawner) for 110 stocks of pink salmon O. gorbuscha, chum salmon O. keta, and sockeye salmon O. nerka with regional‐scale indices of coastal sea surface temperature, sea surface salinity, and upwelling as well as with a large‐scale index of ocean climate. We examined correlations by month and at multiple lags spanning the periods of spawning, freshwater residence, and early ocean residence of salmon. Survival rates of all three salmon species were related to ocean temperatures just prior to, during, and after out‐migration, which are indicative of the early marine conditions experienced by juvenile salmon. This is consistent with the hypothesis that the early marine period is critical to the survival of juvenile salmon. However, survival rates of sockeye salmon were most strongly correlated with coastal sea surface temperature during freshwater residency (i.e., the winter and spring prior to out‐migration). Survival rates of pink salmon were also related to sea surface salinity conditions prior to out‐migration. There was no evidence for any relationship between the survival rates of salmon and coastal upwelling conditions. As in previous studies, we found that correlations between the survival rates of pink or sockeye salmon in Alaska and sea surface temperature have opposite signs from correlations for stocks in British Columbia and Washington at most lags and at both regional and large (basinwide) spatial scales. In general, however, the measures of coastal ocean conditions that we examined explain a relatively small proportion of the environmentally induced variability in salmon survival rates.

Distribution of diatom surface sediment assemblages within Effingham Inlet, a temperate fjord on the west coast of Vancouver Island (Canada)

Twenty-nine surface sediment samples from Effingham Inlet, a small fjord on the west coast of Vancouver Island, British Columbia, were analyzed for diatoms. This fjord has been selected for paleoceanographic investigation due to the presence of laminated sediments resulting from the dysoxic to anoxic bottom water conditions in the inner and outer basins of the inlet. Distributional patterns of the diatom microflora reflected proximity to littoral regions, phytoplankton production, and marine influence from outside the fjord. Principal components and cluster analyses of the microflora established four diatom assemblages with a clear separation between the inner and outer basin diatom floras. Inner basin stations were characterized by elevated absolute abundance with assemblages dominated by spring–early summer bloom taxa including Skeletonema costatum, Thalassiosira nordenskioeldii, and Thalassiosira pacifica. Chaetoceros spp. resting spores were abundant throughout Effingham Inlet, with the exception of the stations closest to the fjord head. Stations located in the outer basin and towards the fjord mouth had relatively lower absolute abundance yet showed a higher relative and absolute abundance of Thalassionema nitzschioides, Rhizosolenia setigera, Coscinodiscus radiatus, Ditylum brightwellii, Odontella longicruris, and Paralia sulcata in relation to the inner basin. Many of these latter taxa are often associated with late summer and autumn conditions in fjords along coastal British Columbia. Oceanographic data for Effingham Inlet suggest that increased offshore penetration is more likely to occur from summer to early fall, with a more restricted offshore influence in the inner basin. Diatom surface sediment assemblages in Effingham Inlet appear to reflect incursions of offshore waters into the fjord. Absolute abundance estimates and the preservation of lightly silicified taxa suggest excellent preservation of fossil material in the sediments of the predominantly anoxic inner basin. Preservation in the outer basin is reduced, reflecting more frequent recharge by oxygenated waters spilling over the outer sill into the basin. Our findings suggest the inner basin should be an optimal site for reconstruction of diatom production, with records from the outer basin providing more consistent information about offshore influence and coastal upwelling conditions over the Holocene. Estimates of diatom abundance within the inner basin sediment may serve as a good proxy of production, although proxy tracers of bottom water conditions and sedimentological analyses must be coupled to the diatom record to ensure depositional conditions were not influencing valve preservation or abundance. Our results suggest that fjords can serve as good environments for paleoceanographic reconstructions of both inshore and offshore conditions although careful site selection and understanding of processes affecting the microfossil record are essential.

Coastal upwelling in the Canary Island region: spatial variability reflected by the surface sediment diatom record

Modern diatom and C org distribution patterns were investigated in 39 surface sediment samples of the Canary region in order to quantitatively determine the influence of coastal upwelling and Saharan dust on the flux of these sedimentary components. High diatom abundance in surface sediments (>2×10 6 valves g −1 dry sediment) as well as the dominance of the assemblages by spores of Chaetoceros, which is a genus related to upwelling conditions, reflect the stronger coastal upwelling conditions occurring at Cape Ghir off the NW African coast. Further offshore, total diatom abundance decreases one order of magnitude (±1×10 5 valves g −1 dry sediment) and the assemblages are dominated by oceanic species of the genus Nitzschia and fresh water diatoms, mainly the genera Aulacoseira, which is known to be a component of Saharan dust. This association suggest that offshore diatom concentrations may be generated by dust input from desert regions. Even though the sediments are expected to preserve only a mixed and averaged oceanographic signal, characteristic biogeographic patterns of a phytoplankton community occurring across a gradient of turbulence and nutrient availability, are recorded in surface sediments off Cape Ghir. This is seen in the subsequent maximum abundances of the genera Thalassiosira, Chaetoceros and Rhizosolenia.

Phytoplankton size-structure, particulate and dissolved organic carbon production and oxygen fluxes through microbial communities in the NW Iberian coastal transition zone

Contrasting hydrographic regimes were studied in the NW Iberian coastal transition zone in order to gain understanding of the relationship between planktonic community structure, production and loss rates, by concurrently measuring size-fractionated phytoplankton biomass and carbon incorporation as well as dissolved organic carbon production and dark respiration by micro- bial communities. Sampling was carried out in August 1998 and October 1999 at a series of stations representing vertical stratification and coastal upwelling conditions in summer, and vertical mixing and shelf-break poleward flow situations during the autumn. A close relationship was found between size-fractionated phytoplankton biomass and production, the relative allocation of total photosynthe- sis to dissolved and particulate organic carbon fractions, and the balance between production and respiration. Picoplankton-dominated communities showed net heterotrophic metabolism and were associated with relatively high rates of DOC production with respect to total carbon incorporation (>15%). In contrast, in coastal upwelling stations, where >2 µm cells dominated, less than 10% of total fixed carbon flowed to DOC, and the net metabolism of the microbial plankton community was autotrophic.

Wind-driven mixed layer and coastal upwelling processes off the south coast of South Africa

Most coastal mixed layer and upwelling investigations have concentrated on the more important fisheries regions situated on the west coasts of the continents, while this paper analyzes conditions on the zonally-orientated south coast of South Africa. Most of the data originate from a short measurement program in the southern summer of 1995, involving both CTD measurements from a small boat and data from a temperature array and coastal sea surface temperature (SST). Limited mixed layer statistics are derived and yield results similar to those of Lentz (1992), although a lack of current measurements precludes any assessment of the Ekman drift. It is shown that the nature of the summer wind forcing is very different to the situation off the South African west coast, with wind variability occurring on much shorter time scales from 2 to 6 days: this has important consequences for plankton blooms and is a likely reason why production is not as efficient off this coast. Past results (Tilney et al., 1996) have shown the importance of coastal trapped waves at depth, but it is apparent that very different conditions occur near the surface. It is found that the coastal SST is a very good monitor of wind-forced coastal upwelling conditions, probably because of the abrupt topography. Substantial baroclinic tidal signals are also apparent at times in the temperature measurements.

Mesoscale distribution patterns of diatoms in surface sediments as tracers of coastal upwelling of the Galician Shelf (NW Iberian Peninsula)

Diatom distribution on continental shelf sediments from the upwelling area off Galicia (NW Iberian Peninsula) has been determined in 78 surface sediment samples. Three well defined biofacies with a close relationship to upwelling influence along the coast have been distinguished from both the absolute diatom abundances in the sediments and assemblage diatom composition based on multivariate statistics: Rías Baixas and the shelf areas south and north to Cape Finisterre. Chaetoceros resting spores as well as highest absolute diatom content in the sediments are recorded in the highly productive Rías Baixas where most of the primary production is due to intense upwelling phenomena. The western shelf, south of Cape Finisterre, is characterized by Thalassionema nitzschioides and Thalassiosira cf. leptopus. Both taxa reflect a minor influence of upwelling conditions and productivity related to more persistent nutrient input due to coastal outwelling rather than upwelling. Minor and patchy upwelling conditions as well as lower productivity in the northern shelf are characterized by the lowest absolute diatom content in the sediments and the important increase in relative abundance of the resistant Paralia sulcata. Caution must be taken in the interpretation of Paralia sulcata dominated biofacies in downcore studies since a juxtaposition of discontinuous upwelling conditions and dissolution effects may be the factors responsible for the relative increase on the taxon in the sediments. The obtained results show the extent and limitations of fossil diatom distribution in surface sediments as tracers of regional coastal upwelling conditions in continental shelves where the existence of extensive areas of relict sediments and transported diatoms may mask the present-day upwelling signal of the photic zone.

Nutrients and trace metals in the northwestern Mediterranean under coastal upwelling conditions

Salinity, temperature, turbidity, nutrients and iron, manganese and copper were measured in 50 surface water samples collected from the Rhoˆne river and river plume, the Gulf of Lions and along a vertical profile in the open northwestern Mediterranean. The data obtained bring new information on the distribution of nutrients and trace metals in the northwestern Mediterranean under wind induced coastal upwelling. Persistent northwesterly winds lead to complex physical processes such as upwelling along the northwestern coast of the Gulf, local eddies and oscillating currents. These processes result in the redistribution of dissolved and particulate components, enriched in the upwelling water, throughout the water column. The effect of nutrient-enriched upwelling water on the primary production of the Gulf is expected to be of secondary importance relative to the river input. In addition to the enhanced wind transport of metal-rich continental dust, the effect of upwelling of the sub-thermocline water and particularly the nepheloid layer has been demonstrated. The behaviour of Fe, Mn and Cu in the mixed water appears to be governed by the common estuarine processes particularly the liquid-solid exchange. Great estuarine reactivity was exhibited by Cu and Mn.

Fluxes of particulate carbon, nitrogen, and phosphorus in the upper water column of the northeast Pacific

Concentrations of carbon, nitrogen and phosphorus were determined in particles that passively sank into multi-replicate collectors set at 50, 250, and 700 m in coastal waters, and 75, 575, and 1050 m in the open ocean. Fluxes as high as 36, 4.1, and 0.19 mmoles of C, N, and P m −2 day −1 were observed at 50 m under coastal upwelling conditions; at 700 m, upwelling period fluxes (9.6, 0.9, and, 0.053 mmoles of C, N and P m −2 day −1) exceeded those measured at 50 and 75 m when samplers were set under low productivity surface waters. 210Pb flux estimates were made on coastal trap particulates. The resulting values were close to the expected and suggest that overall flux estimates are representative of those occuring in the environment. Atomic ratios of C:N:P under upwelling conditions were similar to values reported for living plankton (∼180:18:1), while in the open ocean, atomic ratios of C and N in relation to P were markedly higher (400 to 900:30:1). Fecal pellet fluxes were two orders of magnitude higher under upwelling conditions (∼1 to 3 × 10 5m −2 day −1) than those in the open ocean (∼1000 m −2 day −1). Quantities of passively sinking particulate C, N, and P appeared to be equal to or in excess of the amounts required to meet the nutritional needs of the mid-water zooplankton. Rates of change for C, N, and P and inferred rates of oxygen change varied widely in relation to surface productivity. For example, oxygen utilization rates were as high as 790 μll −1 yr −1 in near-surface waters under upwelling conditions and as low as 4.4 μll −1 yr −1 at mid-depth in the open ocean. Our rates of change, determined by direct measurement, generally agree with previously published estimates from mathematical models.