Main Water Masses Research Articles

A Review of the Oceanography and Antarctic Bottom Water Formation Offshore Cape Darnley, East Antarctica

AbstractAntarctic Bottom Water (AABW) is the densest water mass in the world and drives the lower limb of the global thermohaline circulation. AABW is formed in only four regions around Antarctica and Cape Darnley, East Antarctica, is the most recently discovered formation region. Here, we compile 40 years of oceanographic data for this region to provide the climatological oceanographic conditions, and review the water mass properties and their role in AABW formation. We split the region into three sectors (East, Central and West) and identify the main water masses, current regimes and their influence on the formation of Cape Darnley Bottom Water (CDBW). In the eastern sector, Prydz Bay, the formation of Ice Shelf Water preconditions the water (cold and fresh) that flows into the central sector to E, enhancing sea ice production in Cape Darnley Polynya. This produces a high salinity variant of Dense Shelf Water (DSW) (up to 35.15 g/kg) that we coin Burton Basin DSW. In contrast, the western sector of the Cape Darnley Polynya produces a low salinity variant (up to 34.85 g/kg) we coin Nielsen Basin DSW. The resultant combined CDBW is the warmest (upper temperature bound of 0.05C) AABW formed around Antarctica with an upper bound salinity of 34.845 g/kg. Our findings will contribute to planning future observing systems at Cape Darnley, determining the role that CDBW plays in our global oceanic and climate systems, and modeling past and future climate scenarios.

Sources and composition of organic matter as a tool for understanding the complex variation in paleoenvironments and the connectivity of an epicontinental basin: The Miocene in the northern Pannonian Basin

Epicontinental basins are extremely prone to major paleogeographic changes, and this will directly affect any organic matter (OM) preserved in the depositional record. In this study the Middle–Late Miocene successions in the northern Pannonian Basin System were investigated via sedimentological, petrographic, and geochemical analyses of cores from the Danube Basin to reveal the interplay of factors driving the character of the OM. In the late Middle Miocene (~12.3 Ma), the Central Paratethys Sea maintained normal marine salinity, with dysoxic bottom waters in a distal basin floor environment rich in aquatic OM. The last rifting phase followed during the Late Miocene and led to formation of the deep Lake Pannon. Like seawater, the brackish lake water still also contained sulfate. These open lacustrine deposits (~11.6–10.0 Ma) reveal OM sourced from submerged/floating macrophytes and algae, and humid conditions are indicated by the preponderance of deciduous trees and shrubs on shores. The study identifies hybrid event beds (HEBs) on Lake Pannon's floor (~10.0–9.3 Ma), with currents redepositing mud and OM, resulting in similarities between the Middle Miocene and Late Miocene successions. Turbidite deposition (~9.3–9.0 Ma) from the paleo-Danube induced a shift in OM, replacing algae with terrestrial input. Complete isolation from the main water masses of Lake Pannon (~9.0–8.9 Ma) altered its sources of OM, transitioning from algae to macrophytes, and caused a drop in salinity, likely associated with a humidity peak. The subsequent deltaic dominance (~8.9–8.6 Ma) features well-developed topset lakes, swamps, and floodplain forests, reflecting warm temperate to subtropical climates. The Middle–Upper Miocene deposits studied here are source rocks with fair to very good richness and poor to fair generative potential, and contain kerogen types III and IV, while type II is rare. The rapid paleoenvironmental changes observed over the order of ~100 kyr caused the complete switching of OM type and delivery, giving an indication of the complexity of epicontinental basins.

Influence of Microbial Activities on Fluorescent Dissolved Organic Matter in the Dark Canada Basin Waters

AbstractThe fluorescence characteristics of dissolved organic matter (DOM) were measured to determine the distribution and drivers of DOM in the dark Canada Basin waters. We studied the relationship between fluorescent DOM (FDOM) and apparent oxygen utilization (AOU) in the whole water column as well as in the main water masses (Pacific Winter Water, Atlantic halocline (AH), Atlantic water—Fram Strait and Barents Sea branches, Deep Temperature Minimum, and Canada Basin deep water). The relative water mass fractions of different water masses were estimated using a five end‐members mixing model. The distribution of water mass fractions was found to be in good agreement with the distribution based on the traditional temperature‐salinity diagram. The fractions of AH waters were linked with AOU, highlighting the significant role played by mineralization in shaping AH humic‐like levels. The slope of the relationship between in situ FDOM—AOU was greater than those reported in the other oceans worldwide. This suggests that the AH is a hot spot for microbial mineralization of humic‐like DOM. On the other hand, the relationships with the humic‐like intensities differed among the four humic‐like components in the >125 m waters, indicating distinct environmental dynamics and biogeochemical roles for each humic‐like component.

Latitudinal diversity of planktonic copepods in the Eastern Pacific: overcoming sampling biases and predicting patterns

Gradients of latitudinal diversity are one of the biogeographic features calling the most attention in ecology and macroecology. However, in pelagic communities of the marine environment, geographic trends and patterns are poorly known. We evaluated the latitudinal variation in species richness of marine planktonic copepods in the Eastern Pacific using spatial statistical models and approaches that mitigate and account for biases in occurrence data. A Boosted Regression Tree (BRT) and regression-Kriging based models allowed us to estimate and predict alpha diversity in poorly sampled regions, whereas beta diversity patterns were assessed using generalized dissimilarity analysis (GDM). Species richness showed a bimodal pattern, with a maximum of 291 species in the Northern Hemisphere and Tropical Eastern Pacific Ocean. Particulate Organic Carbon, salinity (max), spatial autocovariate, range of salinity and temperature, and Mixed Layer Depth, explained 85.2% of the latitudinal variability of copepods. Beta diversity was structured into four macrozones associated with the main water masses of the North and South Pacific.Our analytical approaches can overcome the limitations of data gaps, predicting greater diversity in subtropical and coastal areas, while providing insights into key drivers modulating spatial diversity patterns.

Biogeochemistry of dissolved trace metals in the Bay of Bengal

The pronounced seasonal variation over the Bay of Bengal affects trace metals concentration and distribution. Trace metals distribution in the Bay of Bengal has been best characterized during spring and fall intermonsoon, while limited studies were conducted during the southwest monsoon. This study reports the full-depth profiles of trace metals, including dissolved iron, manganese, lead, cadmium, copper, and zinc (Fe, Mn, Pb, Cd, Cu, and Zn) in the Bay of Bengal (BoB) during southwest monsoon, from July to August 2013. At coastal and ocean scales, transect observations covering the entire water depth provided a comprehensive picture of the circulation and biogeochemical cycles of these elements in seawater during the southwest monsoon. Water samples were obtained from one station in the northeastern Indian Ocean (NR-1) and from three shallow coastal stations with maximum depths <60 m (BA-1, BA-3, and BA-5), as well as from three offshore stations with maximum depths exceeding 2000 m (MY-7, MY-9, and MY-11). In the surface layer (5 m depth), the trace metal concentrations at the shallow near-coastal station BA-5 were higher than those at the ocean station NR-1. Surface trace metal concentrations in offshore regions encompassing stations MY-11, MY-9, and MY-7 were relatively higher than those reported for other seasons in a similar salinity region, indicating seasonal variation associated with freshwater intrusion and coastal-derived input. Below the mixed layer depth, the trace metal/phosphate (P) ratio was higher than that previously reported in the eastern Indian Ocean, suggesting an input from continental margins and mildly reducing sediments, particularly for Fe, Mn, and Cu. Moreover, at intermediate depths (190–800 m), where the North Indian Central Water (NICW) is the main water mass, the Cd/P ratio (0.55 ± 0.11 nmol/μmol) deviated from the global trend (∼0.3 nmol/μmol) owing to oxygen-deficient conditions. Intriguingly, at some stations, specifically MY-9 and MY-7, the intermediate dFe concentrations were relatively higher than those at station NR-1 at the same depth. Continental margin sediment, water mass movement, and ventilation may control the transport of Fe from locations with high Fe concentrations, including near the continental shelf (station MY-11 in this study) and the Andaman Sea.

ТЕНДЕНЦИИ ИЗМЕНЕНИЯ ИОННОГО СОСТАВА ЛАДОЖСКОГО ОЗЕРА

The sum of ions of the basic Lake Ladoga water mass has varied quite significantly from 55.6 to 71.6 mg/L over the past 60 years. In the present paper, separate periods of the mineralization growth are identified. It is shown that the change in the mineralization of Lake Ladoga has been always accompanied by a significant change in the ratio of basic ion concentrations. Any significant trends in the total mineralization of Lake Ladoga over the analyzed period have not been identified, but periods of the growth and decrease in the number of ions have been revealed. Until 1998, the periods of increased mineralization, as a rule, were accompanied by an increase in concentrations of SO42 and Cl, most likely coming from the catchment area due to industrial and household pollution. During 2009-2019, the mineralization was growing mainly due to an increase in the absolute and relative concentrations of HCO3. At the same time, the concentration of dissolved CO2 in the main water mass of the lake also was increasing (and, consequently, pH was decreasing). Thus, the changes in the bicarbonate ion concentration in the water of Lake Ladoga may be largely determined by an increase in its inflow from the catchment area, whose possible reason is the enhancement of the chemical weathering of carbonate rocks due to the increasing concentrations of dissolved CO2 in the water.

Hydrological characteristics of the Bering Sea in the summer of 2019

Based on the data of three CTD sections in the northern, northeastern and western Bering Sea of 2019 voyage of Chinese National Arctic Research Expedition (CHINARE), this paper analyzes and studies the hydrological characteristics of the water mass distribution, layered structure, and cline characteristics in different sea areas of the Bering Sea. The results indicate that the hydrological characteristics of the Bering Sea in the summer of 2019 are different from those in the past and that the water mass is warming in many locations. The maximum water temperature reaches 11.13 °C, and the maximum thickness of the warm water is about 32 m. The water mass composition and characteristics of the north-northeast-west sections are significantly different: the BL section has the highest salinity, while the BS section has the lowest salinity, and both the lowest temperature and the largest temperature variation appear in the BL section. The stratification characteristics in all sea areas are noteworthy. In the deep-water seas, there are three types of water masses: upper water (BSW), middle water (BIW) and deep water (BDW) from top to bottom, while two main water masses appear in the shelf waters with the Alaska Coastal Water (ACW) overlies the Bering Sea Shelf Water (BSW). Along the Bering Sea Slope Current (BSC), the water mass is essentially steady. Statically unstable hydrological inversion structure appears near the bottom of the three stations at the northern end of the BL section.

Primary and Bacterial Production in the Bransfield Strait (Antarctica) in Summer

The spatial distribution of the main primary productivity parameters in the Bransfield Strait in the Antarctic summer presents. The integrated primary production in the strait varied from 435 to 741 mgC/m2 per day. The share of primary production in the total production of phyto- and bacterioplankton in the upper 10th layer was 82–91%. Potential photosynthetic capacity (Fv/Fm) was high within the euphotic layer (0.418–0.749) throughout the area. The production parameters in the two main water masses in the strait did not differ. Photosynthetic efficiency (the ratio of the assimilation number and the relative electron transport rate, AN/rETR) varied in different subregions of the study area by almost six times.

Water Masses in the Western Part of the Chukchi Sea in August 2019 and Their Hydrochemical Features

The distribution of water masses in August 2019 in the Chukchi Sea, and their hydrochemical features are i-nvestigated using shipboard data from the transarctic expedition onboard the R/V Professor Levanidov. The work was carried out in the southern shallow part of the sea and in the northern part of the sea outside the 70-meter isobath. Six main water masses were identified: Alaskan and Anadyr Coastal Water (ACW), Siberian Coastal Water (SCW), Melt Water (MW), Summer Bering Sea Water (BSW), Remnant Pacific Winter Water (RWW) and Atlantic Water (AW). Their features are described and analyzed. It was revealed that the water masses of the Chukchi Sea are characterized by a high spatial variability of hydrochemical parameters, especially the BSW, RWW and AW. In the southern part of the Chukchi Sea the presence of very high values of ammonium nitrogen in the bottom layer was noted (up to 12.6 µM). In august 2019, transformed AW, typically residing below 150 m, were observed at a depth of 117–137 meters, characterized by salinity values from 34.2 to 35.7, high content of mineral silicon (93–97 µM), low elevated values of apparent oxygen utilization (240–270 µM), and unusually low N* (a measure of the fixed nitrogen excess relative to phosphorus) values (down to −24.0 µM). At the same time, the AW observed at depths below 140 m did not have such hydrochemical features.

Feeding of walleye pollock and its feeding base in the Chukchi Sea in summer-autumn period

Data on feeding of walleye pollock &lt;i&gt;Gadus chalcogrammus&lt;/i&gt; (3–70 cm long) in the Chukchi Sea in summer-autumn of 2017–2020 are presented. The food base includes zooplankton, benthic invertebrates and fish. The juveniles in the northwestern part of the sea consumed 0.033 t/km2 of prey per day, mainly fish (30.9 %), mysids (20.1 %) and amphipods (13.9 %), whereas the portion of copepods and euphausiids was 5.0–7.6 % of the diet. In the southwestern part of the sea, the juveniles consumption was much higher, as 0.200 t/km2 of prey per day, and included mainly euphausiids and copepods (24.9–51.1%). The adults with length 40–70 cm long dominated in the southwestern Chukchi Sea and consumed on average 13.2 t/km2 of prey per day, shared between fish (42 %), euphausiids (20 %), copepods (6 %), and decapods (11 %). Composition and structure of plankton was different between the main water masses on the shelf occupied the northern and the southern parts of the sea. In the northwestern Chukchi Sea, zooplankton distributed with the mean spatial density of 56.3 t/km2, formed mostly by chaetognaths (35.3 t/km2) and copepods (12.6 t/km2). In the southwestern Chukchi Sea, the mean spatial density of zooplankton was 49.2 t/km2, mostly euphausiids (17.3 t/km2), chaetognaths (15.8 t/km2) and copepods (9.2 t/km2). The total density was close to the level observed in the 2000s, but slight decreasing in biomass of chaetognaths and copepods was observed, mainly due to the recent lack of cold-water species &lt;i&gt;Calanus glacialis&lt;/i&gt;, whereas the biomass of euphausiids, in particularly &lt;i&gt;Thysanoessa inermis&lt;/i&gt;, had almost doubled. Biomass of the main groups of zooplankton prevailing in the diet in the Chukchi Sea in summer-autumn, as copepods and euphausiids, exceeded daily consumption of these groups by walleye pollock in 6–11 times that may indicate a sufficient food supply for this species. Besides, walleye pollock dwelled at the sea bottom and fed on shrimps, gammarids, bottom polychaetes, echiurids, mollusks, and also bottom fish. Total fullness of the pollock stomachs was in the range of 218–228 ‱ that also suggested successful feeding.

Twenty years of in-situ monitoring in the south-eastern Mediterranean Levantine basin: Basic elements of the thermohaline structure and of the mesoscale circulation during 1995-2015

The in-situ data gathered over two decades since mid-1990s in the South-Eastern Levantine Basin from 34 hydrographic campaigns and from 35 bi-weekly and monthly Voluntary Observing Ships (VOS) transects, after the pioneering POEM cruises, have provided insight on the dominant meso-scale coherent circulation features of this sub-basin. The most pronounced feature, the anticyclonic Cyprus Eddy, migrates over the broad region of the Eratosthenes seamount and exhibits significant seasonal and inter-annual spatial-temporal variability. Another prominent structure of the sub-basin is the anticyclonic Shikmona Eddy generated by instabilities of the strong northward flowing jet along the south-easternmost shelf and slope of the Levantine basin. Its evolution and co-existence with the Cyprus Eddy, cause the periodic re-establishment of the Shikmona Gyre, which was first observed during the POEM cruises in mid-1980s. The offshore, cross basin, eastward flowing Mid-Mediterranean Jet (MMJ) defines the northern and southern flanks of these sub-basin scale anticyclonic eddies and transports the lower salinity Modified Atlantic Water (MAW) in the subsurface layer, through the warmest and most saline waters of the Mediterranean. Periodically, the MMJ bifurcates and/or is diverted northward, along the western coast of Cyprus due to westward and northward spatial fluctuations of the Cyprus Eddy’s western boundaries. The current long term in-situ monitoring of the sub-basin provides an overview of the extent of the main water masses and characterizes their variability throughout the period considered. The analysis of the data indicates an increase of the temperature and salinity of the Levantine Surface Water (LSW) and of the subsurface MAW. The Eastern Mediterranean Transient Water (EMTW) is shown to occupy the deep cavities in the vicinity of the Eratosthenes seamount while its upper boundary was found to be lifted to shallower depths over a period of two decades.

Palaeoceanographic and hydrodynamic variability for the last 47 kyr in the southern Gulf of Cádiz (Atlantic Moroccan margin): Sedimentary and climatic implications

AbstractX‐ray fluorescence, grain‐size and oxygen and carbon stable isotope measurements of a 33 m long piston core, recovered from the Pen Duick drift located at the foot of the prominent Pen Duick Escarpment (Atlantic Moroccan margin), are combined to decipher past oceanographic conditions. The data indicate that, similar to the northern Gulf of Cádiz, the Azores Front exerts a major control on the palaeoclimatology of the region. Contrasting the northern Gulf of Cádiz, where Mediterranean Outflow Water is the main water mass at similar water depths, the palaeoceanography of the studied area is mostly influenced by the amount of Antarctic Intermediate Water advected from the south. The density contrast between the Antarctic Intermediate Water and the overlying North Atlantic Central Water determined the strength of the prevailing internal tides and corresponding high current speeds, which drastically impacted the sedimentary record. The most notable impact is the presence of a 7.8 kyr condensed section (30.5–22.7 ka bp). The formation of the Pen Duick sediment drift was not just controlled by the strength of the bottom currents and the intensity of the internal tides, but also by the amount of (aeolian) sediment supplied to the region. Although variable, drift‐growth phases seem to mainly occur during colder periods of the last glacial, that is Heinrich and Dansgaard‐Oeschger events during Marine Isotope Stage 3 and late Marine Isotope Stage 2. These periods, characterised by increased aeolian dust supply and higher bottom currents, coincide with a phase of prolific cold‐water coral growth and enhanced coral mound formation as recorded in numerous cores obtained from the southern Gulf of Cádiz. This implies that both records (on and off mound cores) are pivotal to provide the complete picture of the palaeoclimatic and palaeoceanographic conditions in the region.

Inventory of water masses and carbonate system from Brazilian's northeast coast: Monitoring ocean acidification.

This manuscript presents an inventory of the carbonate system from the main water masses comprising the marine current system on Brazil’s northeast coast (South Atlantic Ocean). For this purpose, four transects were conducted with an approximate length of 357 km (each one) through the platform and continental slope of the Sergipe–Alagoas sedimentary basin. Water samples were then collected in vertical profiles measuring from 5 to 1,799 meters depth, totaling 34 stations. Total alkalinity, calcium, and total boron were obtained analytically from these samples and by relationships with salinity. Speciation and concentration of the carbonate system were obtained by means of thermodynamic modeling. The results revealed that the empirical models used to calculate the concentrations of TA, calcium and total boron showed relevant variation when compared to the analytical values (TA: 5.0–6.5%; Ca: 0.4–4.8%; BT: 7.0–18.9%). However, the speciation and concentration of the carbonate system (CA, DIC, , CO2(aq), ΩCalc, and ΩArag) obtained from the empirical values of TA, calcium and total boron did not differ significantly from those obtained analytically (0.0–6.1%). On the other hand, the parameters of pH, , , CO2(aq), ρCO2, ΩCalc, and ΩArag varied significantly within the different water masses (p < 0.05). This study supports and encourages acidification monitoring projects in the South Atlantic Ocean, based on modeling the carbonate system parameters generated in real-time.

Flow Pathways of Abyssal Water in the Yap Trench and Adjacent Channels and Basins

Abyssal flow pathways in the Yap Trench and adjacent regions were investigated by computing geostrophic flows and analyzing water properties. Using boundary values of potential temperature, salinity, oxygen, and silicate, the upper and lower Circumpolar Deep Waters (UCPW, LCPW) were identified as the main abyssal water masses in the trench. At the western East Mariana Basin, some of the LCPW enters the southern Mariana Trench, and the remainder reaches the northern basin and then partly turns to the northern Mariana Trench, eventually joining the southern trench. At the Yap-Mariana Junction, some LCPW enters the West Mariana Basin, and the remainder passes the region east of the Yap Trench and then flows or subsides to the northern and southern trenches, respectively. In the northern trench, the LCPW flows north into the West Mariana Basin. The UCPW enters the northern Yap Trench via the East Mariana Basin and the Mariana Trench, reaches the sill of the Yap Trench via the East Caroline Basin and a narrow channel, and enters the southern trench via the East/West Caroline and Philippine Basins. The UCPW and LCPW circulate anticlockwise in the southern trench and in the northern region of it, respectively. The LCPW may be driven by the downwelling in the trench.

Pelagic Bacteria and Viruses in a High Arctic Region: Environmental Control in the Autumn Period.

Simple SummaryMicrobial plankton represent a pivotal component of aquatic ecosystems worldwide. Despite their importance in pelagic ecosystems, microbial assemblages are less studied, in many Arctic regions. The study was concerned with the abundance of marine bacteria and viruses, in relation to a set of environmental variables, after the main productive season. We found a mosaic horizontal distribution of the microbial plankton, while the number of bacteria and viruses decreased with depth. Nutrients and zooplankton carbon were significant drivers of microbial abundance. Bacterioplankton abundance was positively correlated with counts of viruses, indicating close relations between these groups of microbes. Comparisons with previous studies revealed strong seasonal variations in the total abundance of marine bacteria, with the maximum values being in the summer and spring periods, while virioplankton counts were comparable in the autumn and spring–summer seasons. Our study is the first report regarding microbial plankton in the northeastern Barents Sea, in the autumn period, and provides baseline information, expanding current knowledge on the structure of pelagic Arctic ecosystems.In the marine environment, bacteria and viruses play a significant role in carbon fluxes, remineralization processes, and the infection of various organisms. We performed a survey in the northeastern Barents Sea, a region adjacent to the Arctic Ocean, to investigate spatial patterns of microbial plankton, after the main productive period, in October 2020. Two main water masses occurred in the study region—colder Arctic Water and warmer Barents Sea Water, representing transformed Atlantic Water. Multivariate analyses detected patchiness in the horizontal distribution of bacteria and viruses, and their abundances showed no clear association with the water masses. There was an obvious vertical pattern in microbial concentration, with the highest estimates in the upper layers. Surface viral and bacterial abundance varied in a wide range (2.20 × 105–10.7 × 105 cells·mL−1 and 0.86 × 106–14.98 × 106 particles·mL−1, respectively) and were correlated with each other. Bacterioplankton was dominated by small-sized cells (<2 μm, 0.04–0.06 µm3), and the average volume of bacterial cells tended to increase toward the seafloor. The ratio of viral to bacterial abundance (VBR) was 11 ± 1 and did not differ between water masses and depth layers. VBR were higher, compared to summer values, suggesting a strong impact of viruses on bacterioplankton, after the main productive season. Redundancy and correlation analyses showed that inorganic nutrients (nitrate and phosphate) and organic carbon from zooplankton were most responsible for the total variability in the microbial parameters. Water temperature and salinity, also, had a measurable impact, but their influence was lower. Bacterial abundance was lower than in other seasons and regions of the Barents Sea, while viral abundance was comparable, suggesting a stronger viral impact on Arctic marine bacteria in the autumn season.

COASTAL OCEAN ACIDIFICATION IN BRAZIL: A BRIEF OVERVIEW AND PERSPECTIVES

This perspective paper aims at presenting the current knowledge on the processes of ocean acidification (OA) and coastal acidification (CA) in the Brazilian coastal ocean. We define and differentiate the processes of OA and CA: the first driven by the actual global increase of atmospheric carbon dioxide (CO2); the second driven by a combination of ocean uptake of atmospheric CO2 and other local/regional chemical additions or subtractions in aquatic ecosystems at the land-ocean interface. Regarding OA, we have centered our analysis on the data available for the main water masses along the Brazilian coast: South Atlantic Central Water (SACW), Tropical Water (TW), and Coastal Water (CW). The few data available for the shallow coastal waters (&lt; 200 m depth) of the continental shelf reveal an increase in the anthropogenic component of the total dissolved inorganic carbon (DIC) pool in the SACW, with a decline in the ocean pH (over two decades; 1993-2013), and in the saturation state of calcium carbonate (CaCO3) minerals. We could not find OA trends for TW and CW because no data was available. Overall, the colder water masses (SACW, Plata Plume) have lower buffering capacity and simulations show that will potentially experience earlier negative OA impacts than the warmer waters masses (TW, Amazon Plume). Regarding CA, we have identified some local/regional studies investigating the carbonate chemistry in nearshore/estuarine ecosystems, particularly on the quantification of sources and sinks of CO2 , and determining short-term variabilities. Apparently, spreading coastal eutrophication in Brazil can enhances or reduces the process of OA, depending on the net ecosystem metabolism in combination with other chemical alterations. However, we could not find medium-long term acidification trends due to the limited data. There is a limited capacity to produce long time-series of carbonate chemistry parameters in key ecosystems and regions along the Brazilian coast. This lack of past information hinders and impairs the scientific community for identifying potential patterns of acidification along the Brazilian coast. We call for an urgent action in Brazil, with emphasis on the establishment of moored buoys/stations and/or scientific programs in the long term with continuous, real-time measurements of the main carbonate chemistry parameters.&#x0D; Keywords: ocean acidification, coastal acidification, coastal eutrophication, continental shelf, Southwestern Atlantic Ocean

Water masses distribution offshore the Sabrina Coast (East Antarctica)

Abstract. Current glacier melt rates in West Antarctica substantially exceed those around the East Antarctic margin. The exception is Wilkes Land, where for example Totten Glacier underwent significant retreat between 2000 and 2012, underlining its sensitivity to climate change. This process is strongly influenced by ocean dynamics, which in turn changes in accordance with the evolution of the ice caps. Here, we present new oceanographic data (temperature, salinity, and dissolved oxygen) collected during austral summer 2017 offshore the Sabrina Coast (East Antarctica) from the continental shelf break to ca 3000 m depth. This area is characterized by very few oceanographic in situ observations. The main water masses of the study area, identified by analysing thermohaline properties, are the Antarctic Surface Water with potential temperature θ&gt;-1.5 ∘C and salinity S&lt;34.2 (σθ&lt;27.55 kg m−3), the Winter Water with -1.92&lt;θ&lt;-1.75 ∘C and 34.0&lt;S&lt;34.5 (potential density, 27.55&lt;σθ&lt;27.7 kg m−3), the modified Circumpolar Deep Water with θ&gt;0 ∘C and S&gt;34.5 (σθ&gt;27.7 kg m−3), and Antarctic Bottom Water with -0.50&lt;θ&lt;0 ∘C and 34.63&lt;S&lt;34.67 (27.83&lt;σθ&lt;27.85; neutral density γn&gt;28.30 kg m−3). The latter is a mixture of dense waters from the Ross Sea and Adélie Land continental shelves. Such waters are influenced by the mixing processes they undergo as they move westward along the Antarctic margin, also interacting with the warmer Circumpolar Deep Water. The spatial distribution of water masses offshore the Sabrina Coast also appears to be strongly linked with the complex morpho-bathymetry of the slope and rise area, supporting the hypothesis that downslope processes contribute to shaping the architecture of the distal portion of the continental margin. Oceanographic data presented here can be downloaded from https://doi.org/10.25919/yyex-t381 (CSIRO; Van Graas, 2021).

Seasonal Transformation and Spatial Variability of Water Masses Within MacKenzie Polynya, Prydz Bay

AbstractWe provide a detailed description of the spatial distribution, seasonality and transformation of the main water masses within MacKenzie Polynya (MP) in Prydz Bay, East Antarctica, using data from instrumented southern elephant seals. Dense Shelf Water (DSW) formation in MP shows large spatial variability that is related to the (a) local bathymetry, (b) water column preconditioning from the presence/absence of different water masses, and (c) proximity to the Amery Ice Shelf meltwater outflow. MP exhibits sustained sea ice production and brine rejection (thus, salinity increase) from April to October. However, new DSW is only formed from June onward, when the mixed layer deepens and convection is strong enough to break the stratification set by Antarctic Surface Water above and Ice Shelf Water below. We found no evidence of DSW export from MP to Darnley polynya, as previously suggested. Rather, our observations suggest some DSW formed in Darnley Polynya may drain toward the western Prydz Bay. Then, DSW is exported offshore from Prydz Bay through the Prydz Channel. The interplay between sea ice formation, meltwater input, and sea floor topography is likely to explain why some coastal polynyas form more DSW than others, as well as the temporal variability in DSW formation within a particular polynya.

Living benthic foraminiferal assemblages of a transect in the Rockall Trough (NE Atlantic)

Foraminifera are unicellular protists and play a major role in the deep-sea ecosystems. This study focusses on the faunal analysis of living benthic foraminiferal assemblages and their vertical distribution along a transect in the Rockall Trough in the NE Atlantic. Therefore, seven multicorer cores from the Rockall Trough (RT-1 – RT-7), NE Atlantic, were collected at water depths between 1008 and 2205 m on the RRS Discovery cruise DY051 in spring 2016.Surface sediment samples of the collected material were analysed up to 10 cm sediment depth for living (Rose Bengal stained) benthic foraminifera to gain insight into the recent distribution of the foraminiferal fauna. The cores were sliced from 0 to 3 cm into 0.5 cm intervals and from 3 to 10 cm in 1 cm slices. Sediments were divided into the fractions >125 μm and 125–63 μm by wet-sieving. The analysis showed that stations differed in live assemblages, diversity, abundances and vertical distribution. Standing stock values of 92–168 ind./10 cm2 for the total, 54–130 ind./10 cm2 for the calcareous and 24–59 ind./10 cm2 for the agglutinated assemblages were obtained.Living deep-sea foraminiferal assemblages differed between the three shallower (RT-1 – RT-3) and the four deeper sites (RT-4 – RT-7), indicating that the different water masses could be a main factor controlling the deep-sea benthic fauna in the Rockall Trough. This area is characterised by two main water masses: the upper more saline Eastern North Atlantic Water (ENAW) and the lower North Atlantic Deep Water (NADW).Basically, Nonionella iridea occurred at all sites, while Cibicidoides species (except C. wuellerstorfi) and Melonis barleeanus were limited to water depths between 1008 and 1610 m (RT-1 – RT-3). Soft-shelled foraminifera increased sharply with water depth. Saccamminid sp. 1 contributed significantly to this increasing proportion of soft-shelled individuals with its maximum at 1857 m water depth (RT-5). Further characteristics of this transect include a mass occurrence of Uvigerina mediterranea, which was only present at 1008 m (site RT-1) or Globobulimina sp. 1 with its highest densities at 1610 m (RT-4), where it accounted for 20% of the total living foraminiferal fauna. The general microhabitat preferences where consistent with those of other studies, although the Rockall Trough is a very dynamic region considering food supply or other physical parameters.

Water masses in the Atlantic Ocean: characteristics and distributions

Abstract. A large number of water masses are presented in the Atlantic Ocean, and knowledge of their distributions and properties is important for understanding and monitoring of a range of oceanographic phenomena. The characteristics and distributions of water masses in biogeochemical space are useful for, in particular, chemical and biological oceanography to understand the origin and mixing history of water samples. Here, we define the characteristics of the major water masses in the Atlantic Ocean as source water types (SWTs) from their formation areas, and map out their distributions. The SWTs are described by six properties taken from the biased-adjusted Global Ocean Data Analysis Project version 2 (GLODAPv2) data product, including both conservative (conservative temperature and absolute salinity) and non-conservative (oxygen, silicate, phosphate and nitrate) properties. The distributions of these water masses are investigated with the use of the optimum multi-parameter (OMP) method and mapped out. The Atlantic Ocean is divided into four vertical layers by distinct neutral densities and four zonal layers to guide the identification and characterization. The water masses in the upper layer originate from wintertime subduction and are defined as central waters. Below the upper layer, the intermediate layer consists of three main water masses: Antarctic Intermediate Water (AAIW), Subarctic Intermediate Water (SAIW) and Mediterranean Water (MW). The North Atlantic Deep Water (NADW, divided into its upper and lower components) is the dominating water mass in the deep and overflow layer. The origin of both the upper and lower NADW is the Labrador Sea Water (LSW), the Iceland–Scotland Overflow Water (ISOW) and the Denmark Strait Overflow Water (DSOW). The Antarctic Bottom Water (AABW) is the only natural water mass in the bottom layer, and this water mass is redefined as Northeast Atlantic Bottom Water (NEABW) in the north of the Equator due to the change of key properties, especially silicate. Similar with NADW, two additional water masses, Circumpolar Deep Water (CDW) and Weddell Sea Bottom Water (WSBW), are defined in the Weddell Sea region in order to understand the origin of AABW.