Upwelling Of Water Research Articles

Exploring the role of clouds in offshore wind potential off the US West Coast in a changing climate

Abstract To meet U.S. goals of deploying additional wind energy as part of the decarbonization strategy, wind plants are being planned for the deep water offshore the western U.S. The wind flow in that region is complex due to the proximity to the coast, cold water upwelling, and persistent stratiform clouds that interact with radiation in ways that have the potential to destabilize the atmosphere. That flow has the potential to change with a changing climate. To address these issues, we assess the flow and the clouds in that region using downscaled climate model data, under both historic climate (1975-2005) and projected future (2025-2055) conditions. We note that the climate simulations agree fairly well with the cloud patterns observed by satellite data in the nearshore and offshore regions. We then assess the projected changes in clouds, wind speed, and other important variables, noting that our simulations project that the predominant north/northwesterly low-level jet is expected to strengthen and clouds are likely to be commensurately enhanced, although projected changes are within about 10% of current conditions. Our examination of the dynamics associated with the changes in the climate simulations provides confidence in the dynamical consistency of these projected changes.

Refining the role of bathymetry, hydrodynamics and upwelling at various scales along the coral reefs at Sodwana Bay, South Africa

Hydrodynamics and physical processes that occur at various length and time scales strongly influence coral reefs. Therefore, understanding the interactions between reefs, hydrodynamics and other physical processes is crucial for the maintenance and survival of reef systems. Coral reefs around the world are under increasing threat to global climate change, and additionally coral bleaching is a major concern for the health and survival of these reefs. Some marginal coral reefs are situated in areas where the complex ocean flow patterns interact with topographical features, providing possible refuges to rising ocean temperatures and coral bleaching. A prominent example is the Sodwana Bay coral reef system which has shown resilience to coral bleaching. This resilience has been attributed to cold water temperature anomalies that cause short-term temperature fluctuations on the reefs. This study explores hydrodynamics at various scales around the Sodwana Bay coral reefs and associated short-term temperature anomalies using a flexible mesh hydrodynamic model of the southwest region of the Indian Ocean, nested within a global ocean model. The nested hydrodynamic model better replicates the observed temperature anomalies when compared to the the reanalysis NEMO global ocean model. The higher model resolution around Sodwana results in less numerical mixing and smoothing of the temperature fields in the nearshore region when compared to the reanalysed NEMO global ocean model leading to a better replication of the local hydrodynamics around the Sodwana region. The anomalies investigated were associated with remote upwelling of cold water near the Delagoa Peninsula, followed by advection from the Delagoa Bight towards the Sodwana region. The separation of the strong intermittent southward stream from the Delagoa Peninsula is strongly linked to the upwelling at the Delagoa Peninsula. An analysis of the hydrodynamic patterns during the anomaly periods reveal that when the strong southward stream reattaches to the coastline, it typically does so south of Sodwana. The reattachment of the stream has an inertial effect and pushes the flow of water against the coastline which deflects the flow northwards up past Sodwana resulting in a northward current reversal along the Sodwana coastline which agrees with observed current reversals during the anomaly periods by insitu measurements taken on the Sodwana reefs. The model also revealed that local upwelling occurs within the Sodwana canyons during this event, making the water in the canyons colder than the surrounding water. When the locally upwelled water spreads over the reef system, the anomaly amplitude is enhanced by approximately 20 %.

Why Is the Monsoon Coastal Upwelling Signal Subdued in the Bay of Bengal?

AbstractThe Indian summer monsoon, which brings heavy precipitation to the densely populated Indian subcontinent, plays an important role in the development of a coastal upwelling circulation that brings colder, nutrient‐rich water to the surface. Although the western shores of the Arabian Sea (AS) and Bay of Bengal (BoB) both experience upwelling‐favorable winds during June‐August, only the AS coastline exhibits significant surface cooling. In contrast, the BoB remains warm and its upwelling is characterized by a transient, weak sea surface temperature (SST) response confined to the east coast of India. A weaker mean alongshore wind stress and coastal circulation do not sufficiently explain the lack of SST response in the BoB. Here, we examine other reasons for the differing behavior of these two coastal margins. Firstly, we show that while winds are persistently upwelling‐favorable in the western AS, intraseasonal wind variability in the BoB induces intermittent upwelling. Secondly, the vertical density stratification is controlled by salinity in the BoB, and upwelled waters are saltier, but only marginally cooler than surface waters. By contrast, the density in the AS is temperature‐controlled, and upwelled waters are substantially colder than the surface. Additionally, satellite‐based SST in the BoB does not adequately resolve the upwelling signal. Using a numerical model, we find that salinity stratification has a greater influence on the mean SST, while wind frequency alters near‐shore SST and its temporal variability. This work has implications for the sensitivity of upwelling regions and their response to wind stress and stratification in a warming climate.

Climate refugia in the Great Barrier Reef may endure into the future.

Although global warming is leading to more frequent mass coral bleaching events worldwide, parts of the Great Barrier Reef (GBR) have consistently escaped severe coral bleaching. Modeling and satellite observations show that climate refugia are created by the upwelling of cooler water to the surface through the interactions of tides and currents with dense reef structures. Here, we use a high-resolution nested regional ocean model to investigate the future status of two relatively large refugia. On the basis of model projections under a high-emission scenario, we find that the upwelling mechanisms will stay active in a warming climate, and these regions are likely to remain approximately more than 1°C cooler than surrounding waters until at least into the 2080s, providing thermal relief to corals. Identification and protection of these refugia may help facilitate reef survival and related biodiversity preservation by allowing their corals time to acclimatize and adapt and ultimately provide source populations to replenish the rest of the reef.

Modulation of Surface Seawater CO2 System at 80°E: Impacts of the Positive IOD in 2019

AbstractTo elucidate impacts of an Indian Ocean Dipole (IOD) event on surface seawater CO2 dynamics, we analyzed data collected along the World Ocean Circulation Experiment Hydrographic Program I08 N line (latitudes 20°S–6°N at 80°E) in December 2019, when a strong positive IOD (pIOD) event occurred. After removing the effects of anthropogenic CO2 accumulation, we examined anomalies of the surface seawater CO2 fugacity (fCO2) from the climatology in relation to other marine properties. At latitudes 11°S–6°S, where horizontal advection of upwelled water off Sumatra was observed, dissolved inorganic carbon and total alkalinity, both normalized to a salinity of 35 (nTCO2 and nTA) showed positive anomalies of +11.4 and +8.1 μmol kg−1, respectively. At latitudes 5°S–5°N, where distinct low‐salinity water was observed because of the pIOD, nTCO2 and nTA showed negative anomalies of −4.0 and ‒0.5 μmol kg−1, respectively. The combined effects of the nTCO2 and nTA anomalies on fCO2 made the observed fCO2 anomalies small, +3.2 and −6.6 μatm for 6°S–11°S and 5°S–5°N, respectively, because the direction of the Revelle factor for TCO2 is opposite to that for TA. We estimated that the pIOD modulated the air–sea CO2 flux by +0.45 and −0.55 mmol m−2 d−1 on average within11°S–6°S and 5°S–5°N, respectively. The impacts of the pIOD on the CO2 dynamics could be explained by the anomalous salinity conditions associated with upwelled water and the freshwater balance.

Late Ordovician ironstone and its relation to ocean redox instability, climate and glaciation

AbstractThe Upper Ordovician (Katian) Neda Formation, a phosphatic ironstone, records a widespread but short‐lived shift to ferruginous waters across a vast epicontinental area. Lithofacies and stratigraphic reappraisal indicate that Neda ironstone deposition occurred on a storm‐dominated ramp when coastal upwelling emplaced eutrophic ferruginous waters that mixed with oxygenated surface water. This stimulated primary productivity and precipitated Fe‐(oxyhydr)oxides in the water column that formed phosphorous and iron‐rich mud. Remobilization of iron beneath the seafloor led to the syndepositional authigenic precipitation of P and Fe minerals in the sediment, preferentially coating grains and forming granular ironstone in the top few decimetres of the sediment. The top of the Neda Formation is a pronounced unconformity punctuated by laterite that formed as sea level fell during the Hirnantian Glaciation. The transition from oxygenated to ferruginous conditions that led to ironstone deposition is interpreted to have been caused by an increase in the equator‐to‐pole temperature gradient and concomitant reorganization of thermohaline circulation during the Katian. This intensified upwelling off the Laurentian margin with upwelled waters transported into the midcontinent where ironstone accumulated through the Sebree Trough. The Neda ironstone's deposition coincident with, and potentially caused by, the same drivers as global oceanographic and biotic change during the Late Ordovician both adds greater insight into the major changes in the oceans preceding the Late Ordovician Mass Extinction and Hirnantian Glaciation, and also furthers an emerging model tying ironstone deposition throughout the Phanerozoic to major Earth system events.

Evidence of 2024 Summer as the Warmest During the Last Four Decades in the Aegean, Ionian, and Cretan Seas

The summer of 2024 witnessed record-high sea surface temperatures (SST) across the Aegean, Ionian, and Cretan Seas (AICS), following unprecedented air heatwaves over the sea under a long-term warming trend of 0.46 °C/decade for the mean atmospheric temperature (1982–2024). The respective mean SST trend for the same period is even steeper, increasing by 0.59 °C/decade. With mean summer surface waters surpassing 28 °C, particularly in the Ionian Sea, the southern Cretan, and northern Aegean basins, this summer marked the warmest ocean conditions over the past four decades. Despite a relatively lower number of marine heatwaves (MHWs) compared to previous warm years, the duration and cumulative intensity of these events in 2024 were the highest on record, reaching nearly twice the levels seen in 2018, which was the warmest until now. Intense MHWs were recorded, especially in the northern Aegean, with extensive biological consequences to ecosystems like the Thermaikos Gulf, a recognized MHW hotspot. The strong downward atmospheric heat fluxes in the summer of 2024, following an interannual increasing four-decade trend, contributed to the extreme warming of the water masses together with other met-ocean conditions such as lateral exchanges and vertical processes. The high temperatures were not limited to the surface but extended to depths of 50 m in some regions, indicating a deep and widespread warming of the upper ocean. Mechanisms typically mitigating SST rises, such as the Black Sea water (BSW) inflow and coastal upwelling over the eastern Aegean Sea, were weaker in 2024. Cooler water influx from the BSW decreased, as indicated by satellite-derived chlorophyll-a concentrations, while upwelled waters from depths of 40 to 80 m at certain areas showed elevated temperatures, likely limiting their cooling effects on the surface. Prolonged warming of ocean waters in a semi-enclosed basin such as the Mediterranean and its marginal sea sub-basins can have substantial physical, biological, and socioeconomic impacts on the AICS. This research highlights the urgent need for targeted monitoring and mitigation strategies to address the growing impact of MHWs in the region.

Antarctic sea ice multidecadal variability triggered by Southern Annular Mode and deep convection

Antarctic sea ice exerts great influence on Earth’s climate by controlling the exchange of heat, momentum, freshwater, and gases between the atmosphere and ocean. Antarctic sea ice extent has undergone a multidecadal slight increase followed by a substantial decline since 2016. Here we utilize a 300-yr sea ice data assimilation reconstruction and two NOAA/GFDL and five CMIP6 model simulations to demonstrate a multidecadal variability of Antarctic sea ice extent. Stronger westerlies associated with the Southern Annular Mode (SAM) enhance the upwelling of warm and saline water from the subsurface ocean. The consequent salinity increase weakens the upper-ocean stratification, induces deep convection, and in turn brings more subsurface warm and saline water to the surface. This salinity-convection feedback triggered by the SAM provides favorable conditions for multidecadal sea ice decrease. Processes acting in reverse are found to cause sea ice increase, although it evolves slower than sea ice decrease.

North‐East Peri‐Tethyan Water Column Deoxygenation and Euxinia at the Paleocene Eocene Thermal Maximum

AbstractThe Paleocene–Eocene Thermal Maximum (PETM) is associated with climatic change and biological turnover. It shares features with the Oceanic Anoxic Events (OAEs) of the Mesozoic, such as transient global warming and biogeochemical perturbations. However, the PETM experienced a more muted expansion of marine anoxia compared to the Mesozoic OAEs (especially OAE2), with geographically limited evidence for photic zone euxinia (PZE). We explore the extent and drivers of marine deoxygenation during the PETM using biomarkers for water column euxinia and anoxia as well as an intermediate complexity Earth system model (cGEnIE). These reveal that the water column in the North‐East Peri‐Tethys became anoxic, with euxinic conditions reaching the photic zone (PZE) during the PETM. Our model shows that euxinia developed due to a global increase in the ocean nutrient inventory with concomitant oxygen consumption, similar to findings for OAE2. The particularly strong regional response in the NE Peri‐Tethys appears to arise from a combination of global CO2‐weathering forcing, regionally restricted circulation and upwelling of sulphidic thermocline waters. Unlike OAE2, anoxia and PZE do not become widespread in our PETM simulations, consistent with new and existing geochemical and biological proxy data. This globally muted response could result from reduced biogeochemical feedbacks to climate forcing relative to the mid‐Cretaceous climate. Our observations suggest that similar mechanisms operated in response to disparate Cenozoic (PETM) and Mesozoic (OAEs) transient global warming events, while also highlighting that background conditions are crucial in modulating the sensitivity of Earth's system to them.

Yucatan shelf’s larval density and distribution of Auxis spp. and Caranx crysos are primarily driven by regional upwelling and seasonality

The extensive Yucatan Shelf (YS) in the southern Gulf of Mexico provides habitat for many marine species and supports important fisheries. A striking feature is the regional upwelling along its eastern margin due to the interaction of the Yucatan Current with the western slope of the Yucatan Channel. Coupled with easterly winds, the upwelled water fertilizes the shelf and contributes to high productivity in an otherwise oligotrophic region. However, an understanding of the role that regional upwelling plays on fish spawning and larval fish distributions is limited. We describe the distribution, frequency of occurrence, and densities of two commercially important neritic species (Auxis spp. and Caranx crysos) with contrasting life histories (different adult habitat, neritic vs. neritic and oceanic, and with spawning peak vs. year around spawner). The relationship between larval density and environmental variables, including upwelling indicators, was examined for three oceanographic cruises that covered the entire YS and which were held during summer through fall (2015, 2016 and 2018). None (Auxis spp.) or very few (C. crysos) larvae were caught during the late fall cruise in November. The highest densities of both taxa were found during the summer cruise in July, consistent with their spawning periods. Both species were mostly distributed beyond the 40 m isobath, and the highest densities were found over the central and eastern shelf. Generalized additive models indicated that Auxis spp. and C. crysos densities were correlated with low chlorophyll a concentration (located in the outer shelf) and a shallower 22.5 °C isotherm (a proxy for upwelling), indicating that regional upwelling was associated with higher larval fish densities.

A conceptual and numerical model of fluid flow and heat transport in the Topusko hydrothermal system

Comprehensive understanding of hydrothermal systems is often obtained through the integration of conceptual and numerical modelling. This integrated approach provides a structured framework for the reconstruction and quantification of fluid dynamics in the reservoir, thereby facilitating informed decision-making for sustainable utilisation and environmental protection of the hydrothermal system. In this study, an updated conceptual model of the Topusko hydrothermal system (THS; central Croatia) is proposed based on structural, geochemical, and hydrogeological analyses. The stratigraphic sequence and the structural framework of the THS were defined based on geological maps and field investigations. As depicted by hydrochemical and isotope analyses, thermal waters in Topusko (temperatures of up to 65 °C) are of meteoric origin and circulate in a carbonate aquifer. The THS receives diffuse recharge approximately 13 km S from Topusko, where Triassic carbonates crop out. Gravity-driven regional groundwater circulation is favoured by regional thrusts that tectonically uplifted Palaeozoic low permeable rocks. These structures confine the fluid flow in the permeable, fractured and karstified, Triassic carbonates favouring the northward circulation of the water. A regional anticline lifts the aquifer closer to the surface in Topusko. Open fractures in the anticline hinge zone increase the fracturing and permeability field of the aquifer promoting the quick upwelling of the thermal water resulting in the Topusko thermal springs. Numerical simulations of fluid flow and heat transport corroborate the proposed conceptual model. In particular, a thermal anomaly was modelled in the Topusko subsurface with temperature values of 31.3 °C and 59.5 °C at the surface and at the base of the thermal aquifer, respectively, approaching the field observations. These findings showed that the circulation of Topusko thermal water is influenced by regional and local geological structures suggesting that the enhanced permeability field in the discharge area enables the formation of the natural thermal springs.

Integration of airborne geophysical data for the characterization of the geothermal system in Valle del Cura, high central Andes

The Valle del Cura region, located in the High Central Andes, over the Pampean flat-slab segment, exhibits several geothermal manifestations suggesting structural rather than magmatic controls. However, the structural and favorable conditions of this geothermal system have not been studied in detail yet. By integrating high-resolution airborne geophysical data with existing geological information using GIS tools, we can better characterize the structural controls of the thermal areas. The application of the upward continuation filter and tilt-angle derivative to the reduced to pole magnetic anomaly map allowed us to delineate structural lineaments that correlate well with known faults in the area. Euler deconvolution successfully identified local structures controlling the subsurface water upwelling and provided reliable depth estimations. Results indicate that the Despoblados area is characterized by NW-oriented deep structural controls reaching depths of up to 5 km. In contrast, the Bañitos-Gollete and the northern thermal areas are controlled by the intersection of N-S with E-W shallow structures at less than 3 km deep. Aeroradiometric data provided additional information for the characterization of several lithological units based on the dominance of radioelements (K, Th and U) in near-surface rocks by using individual and ternary maps. In addition, estimations of radiogenic heat production were crucial for assessing the potential energy of geothermal resources in the region. In particular, higher average values were obtained for igneous and metamorphic basement which may contribute to the geothermal gradient and temperature distribution at depth. Further studies, including new geophysical data acquisition and field verification, are still needed to fully describe the regional and local structures involved in these geothermal areas.

Loss of pelagic fish and zooplankton density associated with subglacial upwelling in high Arctic estuaries may be mitigated by benthic habitat expansion following tidewater glacier retreat

Glacier fronts are hotspots of pelagic productivity due to upwelling of nutrient-rich water. As tidewater glaciers retreat into land, this subglacial circulation will disappear and sedimentation from terrestrial runoff will increase, leading to a decrease in pelagic productivity with a decline in the abundance of fish and zooplankton. We used Billefjorden, a high Arctic fjord with a glacier recently transitioned from sea- to land-terminating as a case study to identify spatial differences and small-scale environmental drivers of density and vertical distribution of fish and zooplankton along a gradient of glacier retreat (directly in front of the land-terminating glacier front, a river bay with terrestrial input from land-terminating glaciers further inland and a location with minimal glacial input). We developed a sustainable and efficient protocol to safely sample the glacier front and shallow coastal areas using hydroacoustics and a remote autonomous vehicle combined with oceanographic measurements and baited remote cameras. Over two years, pelagic density was lowest at the now land-terminating glacier front and highest at the site with lowest terrestrial input. Temperature, depth and turbidity explained less than 8% of the variation each.

LARGE-SCALE LANDSLIDES DUE TO SALINE WATER PLUME INTRUSION - AN EXAMPLE OF THE OKIMI LANDSLIDE IN NIIGATA PREFECTURE, JAPAN

Large-scale landslides with volumes ranging from tens to hundreds of millions of m3 are scattered throughout Niigata Prefecture, Japan. There is no accepted theory, although many researchers have argued about the mechanism of these landslides. Highly concentrated Na-Cl type groundwater (hereafter called "saline water") has often been found in large-scale landslides in Niigata Prefecture. In addition, the observation wells where saline water occurs are sometimes flowing wells. We also pay special attention to the distribution of landslide-prone areas and oil and gas fields in Niigata Prefecture, which generally overlap, and saline water from landslides is originally fossil seawater such as oil-brine based on geochemical characteristics. On the other hand, anomalous high-pressure reservoirs at depths of more than 1,000 m in oil and gas fields have been known since the 1960s and are possible saline water sources. We believe saline water's behavior is key to better understanding the mechanism of large-scale landslides. The Okimi landslide, this research area, is located in the Kamiya area, Joetsu City, western part of Niigata Prefecture, Japan. The aspect of the active body is about 500 m wide and 1,500 m long, with an area of about 70 ha. The bedrock geology is mainly Neogene unconsolidated mudstone. According to previous studies, saline water has been detected in observation wells at the head of this landslide. Since the geological formation containing saline water has a considerably low resistivity value (≤ 2.0 Ωm), the CSMT method is best suited for electromagnetic exploration to visualize the resistivity up to 1,000 m depth. The survey results confirm the existence of a saline water plume rising from a "saline water chamber" located 100 to 300 m below the western side of this landslide to the bottom of this landslide (at a depth of about 30 m). The presence of the saline water plume suggests that the upwelling of saline water from the anomalous high-pressure reservoir (saline water chamber) is closely related to several large-scale landslides.

Acoustic vector sensing reveals ecologically modulated sympatry of blue and fin whales

Earth’s largest animal species, blue and fin whales, share a similar life history strategy involving annual long-distance migration between foraging and breeding habitat. The difficulty of monitoring spatial distributions of both species simultaneously has limited understanding of their sympatry within foraging habitats that sustain them. In addressing this observational challenge, a valuable method is acoustic vector sensing of the sounds produced by the whales. Using three years of continuous acoustic vector sensor data, we examine habitat occupancy of blue and fin whales in the central California Current Ecosystem. While fin whales called almost exclusively from offshore deep-water habitat, blue whales called predominantly from shelf and slope water habitat—indicating an allopatric tendency. However, stronger sympatry occurred during the third year, as blue whales spent a greater proportion of time in offshore deep-water habitat. This year was distinguished by the strongest wind-driven coastal upwelling, the furthest offshore extension of upwelled waters, and the greatest abundances of krill that are prey of both whale species. upporting the recovery of endangered blue and fin whale populations requires understanding where and how they live, and acoustic vector sensing is effective for this purpose in ecological research and resource management.

Impact of tropical cyclone Biparjoy on oceanic parameters in the Arabian Sea

Climate change is expected to intensify tropical cyclones (TCs), requiring a deeper understanding of their ecosystem impacts. This study investigated TC Biparjoy impact on parameters from June 6 to 19, 2023, using satellite and vertical profiles. Initially, Chlorophyll-a levels remained steady but surged above 4 mg/m3 after the high-intensity phase, indicating increased phytoplankton biomass. Sea surface temperature (SST) initially exceeded 32 °C, favoring cyclone intensification, but dropped below 26 °C post-high-intensity phase due to mixing and upwelling of cooler waters. The SST gradient exceeded 0.15 °C/km post-cyclone. Elevated sea surface height around 0.5 m offshore and over 1 m along the coast was recorded. Wind stress values exceeding 0.4 N/m3 were observed during the high-intensity phase. Vertical profile showed uplifted low-temperature, nutrient-rich waters, enhancing phytoplankton productivity, supported by increased nitrate (>10 mmol/m3) and phosphate (>1.2 mmol/m3) levels. Additionally, slight increase in DIC, and pH during the cyclone period suggested changes in biogeochemical processes.

Formation mechanisms and biogeochemical response of coastal salinity front in the central eastern Arabian Sea

This study investigates the formation mechanisms and impact of a coastal salinity front observed in the central eastern Arabian Sea (EAS) coast, particularly off Mangalore (∼13°N), during the peak summer monsoon in August 2018. The interplay of intense monsoon rainfall, river runoff and coastal upwelling created a dynamic frontal zone characterised by distinct physical and biogeochemical properties in the central EAS. The study revealed that observed salinity fronts are formed due to the breaking of freshwater lenses by strong upwelled waters and the subsequent offshore transport of low-salinity plumes by prevailing current and Ekman transport. The high nutrient concentrations enhanced the chlorophyll a concentration 15–20 times higher (10.12 mg/m3) in the frontal zone compared to the non-frontal station. The dominance of diatoms in the frontal zone indicates herbivorous control in the coastal food web. Accumulation of plastic debris and foam-like particles in the frontal zone poses ecological risks and threatens aquatic life.

Cryophilic polychaetes at the subtropical Laurentian margin of the Iapetus Ocean: Evidence for cold-water ocean circulation and upwelling

Abstract Through the Phanerozoic eon, the trace fossil Macaronichnus—made by sediment-burrowing polychaetes—appears to be restricted to intermediate- and high-latitude shallow-marine habitats with cold to temperate waters or coastal areas closer to the equator with cold-water upwelling. We present records of such trace fossils in Ordovician (Darriwilian–Sandbian?) shallow- and deep-water marine deposits in the Central Norwegian Caledonides, pointing toward previously undocumented deep-ocean circulation and upwelling of cold water along the subtropical eastern Laurentian margin and adjacent volcanic arcs and microcontinents in the early Paleozoic Iapetus Ocean. Possible implications for Middle Ordovician ocean circulation patterns are discussed in relation to paleogeographic reconstructions and paleoclimatic models.

Analysis of the latitudinal and longitudinal (coastal and pelagic zones) variability of coccolithophore assemblages in the water column of the Western Iberian Margin in late summer of 2022

This study investigates the abundance, composition, and biogeographical distribution of coccolithophores in the water column of the northwestern Iberian coastal upwelling system during late summer 2022. Coccolithophore data were compared with in situ measurements of physical, chemical, and biological parameters, as well as with satellite data and the upwelling index (UI) for the study area. Canonical Correspondence Analysis (CCA) was performed to determine the relationships between coccolithophore assemblages and environmental variables. The results reveal a latitudinal and longitudinal gradient in coccolithophore abundance, with higher concentrations towards the north and east, indicating a stronger influence of coastal upwelling near the coast (stations CA-7, CA-8, CA-4). Our data suggest that the source of upwelled water in the north (Eastern North Atlantic Central Waters of subpolar origin, ENACWsp) differs from that in the south (ENACWst, of subtropical origin). Significant correlations between UI and the total abundance of coccoliths and coccospheres underscore the role of upwelling in coccolithophore distribution. Additionally, correlations with fluorescence and turbidity indicate that coccolithophores contribute substantially to primary production in the region. Certain species are proposed as paleoenvironmental indicators due to their affinity for specific environmental conditions. The small Noëlaerhabdaceae group (small Gephyrocapsa group + Emiliania huxleyi) serves as a proxy for primary productivity and intense upwelling, while Florisphaera profunda is associated with upwelling relaxation and low productivity. Discrepancies with satellite data are attributed to their limitations in detecting subsurface biological processes. This study also supports the use of the N-ratio in water column samples, not just in sediments, and improves the understanding of primary productivity at the Western Iberian Margin during the upwelling season.

Upwelling Enhances Mercury Particle Scavenging in the California Current System.

Coastal upwelling supplies nutrients supporting primary production while also adding the toxic trace metal mercury (Hg) to the mixed layer of the ocean. This could be a concern for human and environmental health if it results in the enhanced bioaccumulation of monomethylmercury (MMHg). Here, we explore how upwelling influences Hg cycling in the California Current System (CCS) biome through particle scavenging and sea-air exchange. We collected suspended and sinking particle samples from a coastal upwelled water parcel and an offshore non-upwelled water parcel and observed higher total particulate Hg and sinking flux in the upwelling region compared to open ocean. To further investigate the full dynamics of Hg cycling, we modeled Hg inventories and fluxes in the upper ocean under upwelling and non-upwelling scenarios. The model simulations confirmed and quantified that upwelling enhances sinking fluxes of Hg by 41% through elevated primary production. Such an enhanced sinking flux of Hg is biogeochemically important to understand in upwelling regions, as it increases the delivery of Hg to the deep ocean where net conversion to MMHg may take place.