Syntheses of carbonate chemistry spatial patterns are important for predicting ocean acidification impacts, but are lacking in coastal oceans. Here, we show that along the North American Atlantic and ...Gulf coasts the meridional distributions of dissolved inorganic carbon (DIC) and carbonate mineral saturation state (Ω) are controlled by partial equilibrium with the atmosphere resulting in relatively low DIC and high Ω in warm southern waters and the opposite in cold northern waters. However, pH and the partial pressure of CO
(pCO
) do not exhibit a simple spatial pattern and are controlled by local physical and net biological processes which impede equilibrium with the atmosphere. Along the Pacific coast, upwelling brings subsurface waters with low Ω and pH to the surface where net biological production works to raise their values. Different temperature sensitivities of carbonate properties and different timescales of influencing processes lead to contrasting property distributions within and among margins.
Ocean acidification is predicted to occur first in polar oceans. We investigated the saturation state of waters with respect to calcite (Ωcal) and aragonite (Ωarg) in six sections along an Arctic ...outflow pathway through the Canadian Arctic Archipelago (CAA) and into the northwestern Atlantic using dissolved inorganic carbon and total alkalinity measurements from 2003 to 2005. The study area, a key region connecting the Arctic and the North Atlantic, includes Smith Sound, Barrow Strait, Baffin Bay, Davis Strait, Hudson Strait, and the Labrador Sea. The average Ωarg in the Arctic outflow was 1.18 ± 0.17 in Barrow Strait and 1.31 ± 0.14 in Smith Sound, with areas where Ωarg < 1. The Arctic outflow through the CAA has a high content of Pacific waters, which have a low saturation state. These waters can be traced along the western Baffin Bay to Davis Strait. South of Davis Strait, this outflow is modified by mixing with slope and offshore waters of Atlantic origin and with the outflow from Hudson Strait. Despite the mixing, low saturation state water can still be identified on the southern Labrador Shelf. The aragonite saturation horizon is found at ∼150 m in Barrow Strait; at 200 m in Baffin Bay, Davis Strait, and Hudson Strait; and at 2300 m in the Labrador Sea. This study provides baseline data of the saturation states for the waters of the CAA and the northwest Atlantic. It also illustrates the downstream evolution of low saturation state Arctic outflow in the northwest Atlantic.
Freshwater transport through Davis Strait can supply additional buoyancy to the deep convection region of the Labrador Sea which influences the strength of the meridional overturning circulation and ...consequently the global climate. The freshwater contribution from local sea ice meltwater, meteoric water (fluvial, glaciofluvial and precipitation) and the Arctic outflow were quantified using oxygen isotope composition (δ18O), salinity and nutrient relationships in September–October, 2004. Freshwater transported by the Arctic outflow was isolated using a modified nutrient relationship method and further deconvoluted into sea ice meltwater, meteoric water and Pacific water. For the first time, fluxes of individual freshwater components were estimated using observations of the velocity field derived from mooring arrays and geostrophic currents from hydrography. The Arctic outflow dominated in western Davis Strait (>60%) and its influence extended eastward close to the Greenland Slope. The sea ice meltwater fraction was small (<2%) and limited to the surface layer of the central and western Strait. The meteoric water fraction was highest on the Greenland Shelf (>6%) and attributed to glacial meltwater. The freshwater inventory of the 0–100 m layer was equivalent to 7.4 m in western Davis Strait: 8 m from the Arctic outflow and −0.6 m from brine rejection. In eastern Davis Strait, the freshwater inventory was 4 m: 3 m from meteoric water and 1 m from sea ice meltwater. The Arctic outflow contributed 82–99 mSv to the southward freshwater transport about 67–81% of the total; glacial meltwater contributed the largest northward transport of 10–30 mSv.
Key Points
Application of a new method to quantify Arctic Water in the northwest Atlantic
Estimate of composition and fluxes of freshwater through Davis Strait
Dominant southward flow by Arctic outflow, northward flow by glacial meltwater
Climate change affects the Arctic with regards to permafrost thaw, sea-ice melt, alterations to the freshwater budget and increased export of terrestrial material to the Arctic Ocean. The Fram and ...Davis Straits represent the major gateways connecting the Arctic and Atlantic. Oceanographic surveys were performed in the Fram and Davis Straits, and on the east Greenland Shelf (EGS), in late summer 2012/2013. Meteoric (f
), sea-ice melt, Atlantic and Pacific water fractions were determined and the fluorescence properties of dissolved organic matter (FDOM) were characterized. In Fram Strait and EGS, a robust correlation between visible wavelength fluorescence and f
was apparent, suggesting it as a reliable tracer of polar waters. However, a pattern was observed which linked the organic matter characteristics to the origin of polar waters. At depth in Davis Strait, visible wavelength FDOM was correlated to apparent oxygen utilization (AOU) and traced deep-water DOM turnover. In surface waters FDOM characteristics could distinguish between surface waters from eastern (Atlantic + modified polar waters) and western (Canada-basin polar waters) Arctic sectors. The findings highlight the potential of designing in situ multi-channel DOM fluorometers to trace the freshwater origins and decipher water mass mixing dynamics in the region without laborious samples analyses.
This study investigates the biogeochemical drivers of aragonite saturation state (ΩAr) in Baffin Bay, with a focus on the relatively undersampled west Greenland shelf. Our findings reveal two main ...depth‐dependant processes controlling the spatial distribution of ΩAr in Baffin Bay; within the upper 200 m, lower ΩAr coincides with increasing fractions of Arctic‐outflow waters, while below 200 m organic matter respiration decreases ΩAr. A temporal analysis comparing historical measurements from 1997 and 2004 with our 2019 data set reveals a significant decrease in the ΩAr of Arctic‐outflow waters, coinciding with reduced total alkalinity (TA). However, no discernible anthropogenic ocean acidification signal is identified. Significant Arctic water fractions (20%–40%) are found to be present on the west Greenland shelf, associated with reduced TA and ΩAr. A numerical modeling simulation incorporating a passive tracer demonstrates that periodic changes in wind direction lead to a switch from onshore to offshore Ekman transport along the Baffin Island current, transporting Arctic waters toward the west Greenland shelf. This challenges the conventional understanding of Baffin Bay's circulation and underscores the need for further research on the region's physical oceanography. Based on salinity‐TA relationships, surface waters on the west Greenland shelf have a significantly lower meteoric TA end‐member compared to waters of the Baffin Island Current in western Baffin Bay. The low eastern TA freshwater end‐member agrees well with recent glacial meltwater TA measurements, suggesting that glacial meltwater is the main freshwater source to surface waters on the west Greenland shelf.
Plain Language Summary
Baffin Bay, with its complex interplay of Atlantic and Arctic water masses, is particularly susceptible to ongoing ocean acidification, mainly due to the presence of relatively fresh and low‐alkalinity Arctic waters. To date measurements of the inorganic carbon system in Baffin Bay have primarily been captured at key entrance and exit gateways, and on the Canadian side of the bay, leaving the west Greenland shelf relatively undersampled. This study provides a bay‐wide perspective of the main factors influencing aragonite saturation state (ΩAr; an indicator of ocean acidification impacts on marine calcifying organisms) across Baffin Bay, including the west Greenland shelf. We found that within the upper 200 m, low ΩAr coincides with increased presence of Arctic waters, while below 200 m the breakdown of organic matter decreases ΩAr. Historical data from 1997 and 2004 compared to our 2019 measurements show a significant drop in ΩAr of Arctic waters, but no clear signal of anthropogenic ocean acidification was observed. Surprisingly, the west Greenland shelf has significant fractions (20%–40%) of Arctic water. A numerical modeling simulation suggests that periodic changes in wind direction can transport Arctic waters from across Baffin Bay, challenging our traditional understanding of the bay's circulation.
Key Points
Increased fractions of Arctic waters decrease aragonite saturation state (ΩAr) in the upper 200 m, while respiration does so below 200 m
Decreased ΩAr of Arctic waters over the last two decades is associated with decreased alkalinity, not additional CO2
Significant fractions of Arctic‐outflow waters on the west Greenland shelf challenges current knowledge of circulation in Baffin Bay
The high abundance of transparent exopolymer particles (TEP) in marine and freshwater greatly affects particle dynamics. TEP act as glue for colliding particles and form the matrix in aggregates, ...thereby altering aggregation dynamics. We studied the sinking behavior of freshly produced, particle-free TEP and of aggregates composed of TEP and latex spheres in a laboratory using water collected from Santa Barbara Channel, California. Particle-free TEP ascend and accumulate in the surface layer of a settling column at an average velocity of $1.6\times 10^{-4}\ \text{cm}\ \text{s}^{-1}$. The estimated density of TEP ranges from 0.70 to 0.84 g cm-3. TEP also transported latex spheres of 45.6 and 1.82 μm in diameter and a density of 1.05 g cm-3 to the surface layer. We describe a simple model illustrating the role of TEP for the vertical transport of solid particles. The densities and relative proportions of TEP, solid particles, and interstitial water within an aggregate determine its sinking or ascending velocity. High ratios of TEP to solid particles retard the sinking of aggregates, prolonging their residence time in the surface ocean. Our results demonstrate that TEP can provide a vehicle for the upward flux of biological and chemical components in the marine environment, including bacteria, phytoplankton, carbon, and reactive trace elements.
Export of nutrients from the Arctic Ocean Torres-Valdés, Sinhué; Tsubouchi, Takamasa; Bacon, Sheldon ...
Journal of geophysical research. Oceans,
April 2013, Letnik:
118, Številka:
4
Journal Article
Recenzirano
Odprti dostop
This study provides the first physically based mass‐balanced transport estimates of dissolved inorganic nutrients (nitrate, phosphate, and silicate) for the Arctic Ocean. Using an inverse ...model‐generated velocity field in combination with a quasi‐synoptic assemblage of hydrographic and hydrochemical data, we quantify nutrient transports across the main Arctic Ocean gateways: Davis Strait, Fram Strait, the Barents Sea Opening (BSO), and Bering Strait. We found that the major exports of all three nutrients occur via Davis Strait. Transports associated with the East Greenland Current are almost balanced by transports associated with the West Spitsbergen Current. The most important imports of nitrate and phosphate to the Arctic occur via the BSO, and the most important import of silicate occurs via Bering Strait. Oceanic budgets show that statistically robust net silicate and phosphate exports exist, while the net nitrate flux is zero, within the uncertainty limits. The Arctic Ocean is a net exporter of silicate (−15.7 ± 3.2 kmol s−1) and phosphate (−1.0 ± 0.3 kmol s−1; net ± 1 standard error) to the North Atlantic. The export of excess phosphate (relative to nitrate) from the Arctic, calculated at −1.1 ± 0.3 kmol s−1, is almost twice as large as previously estimated. Net transports of silicate and phosphate from the Arctic Ocean provide 12% and 90%, respectively, of the net southward fluxes estimated at 47°N in the North Atlantic. Additional sources of nutrients that may offset nutrient imbalances are explored, and the relevance and the pathway of nutrient transports to the North Atlantic are discussed.
Key Points
We provide physically‐based mass‐balanced Arctic nutrient transportThe Arctic Ocean exports silicate and phosphate to the North Atlantic.The Arctic Ocean nitrate budget is balanced.
The freshwater composition of waters on the southeast Greenland shelf and slope are described using a set of high‐resolution transects occupied in summer 2004, which included hydrographic, velocity, ...nutrient, and chemical tracer measurements. The nutrient and tracer data are used to quantify the fractions of Pacific Water, sea ice melt, and meteoric water present in the upper layers of the East Greenland Current (EGC) and East Greenland Coastal Current (EGCC). The EGC/EGCC system dominates the circulation of this region and strongly influences the observed distribution of the three freshwater types. Sea ice melt and meteoric water fractions are surface intensified, reflecting their sources, and generally increase southward from Denmark Strait to Cape Farewell, as well as shoreward. Significant fractions of Pacific Water are found in the subsurface layers of the EGCC, supporting the idea that this inner shelf branch is directly linked to the EGC and thus to the Arctic Ocean. A set of historical sections is examined to investigate the variability of Pacific Water content in the EGC and EGCC from 1984 to 2004 in the vicinity of Denmark Strait. The fraction of Pacific Water increased substantially in the late 1990s and subsequently declined to low levels in 2002 and 2004, mirroring the reduction in Pacific Water content reported previously at Fram Strait. This variability is found to correlate significantly with the Arctic Oscillation index, lagged by 9 years, suggesting that the Arctic Ocean circulation patterns bring varying amounts of Pacific Water to the North Atlantic via the EGC/EGCC.
Studies of marine microbioerosion in polar environments are scarce. They include our recent investigations of bioerosion traces preserved in sessile balanid skeletons from the Arctic Svalbard ...archipelago and the Antarctic Ross Sea. Here, we present results from a third study site, Frobisher Bay, in the eastern Canadian Arctic, together with a synthesis of our current knowledge of polar bioerosion in both hemispheres. Barnacles from 62 to 94 m water depth in Frobisher Bay were prepared using the cast-embedding technique to enable visualization of microboring traces by scanning electron microscopy. In total, six ichnotaxa of traces produced by organotrophic bioeroders were found. All recorded ichnotaxa were also present in Mosselbukta, Svalbard, and most in the Ross Sea. Frobisher Bay contrasts with Mosselbukta in that it is a siliciclastic-dominated environment and shows a lower ichnodiversity, which may be accounted for by the limited bathymetrical range and a high turbidity and sedimentation rate. We evaluate potential key ichnotaxa for the cold-temperate and polar regions, of which the most suitable are Flagrichnus baiulus and Saccomorpha guttulata, and propose adapted index ichnocoenoses for the interpretation of palaeobathymetry accordingly. Together, the three studies allow us to make provisional considerations about the biogeographical distribution of polar microbioerosion traces reflecting the ecophysiological limits of their makers.
The Global Ocean Ship-Based Hydrographic Investigations Program (GO-SHIP) provides a globally coordinated network and oversight of 55 sustained decadal repeat hydrographic reference (core) lines as ...part of the global ocean/climate observing systems (GOOS/GCOS) for study of physical oceanography, the ocean carbon, oxygen and nutrient cycles, and marine biogeochemistry. GO-SHIP enables assessment of the ocean sequestration of heat and carbon, changing ocean circulation and ventilation patterns, and their effects on ocean health and Earth's climate. Rapid quality control and open data release along with incorporation of the GO-SHIP effort in the Joint Technical Commission for Oceanography and Marine Meteorology (JCOMM) in situ Observing Programs Support Center (JCOMMOPS) have increased the profile of, and participation in, the program and led to increased data use for a range of efforts. In addition to scientific discovery, GO-SHIP provides climate-quality observations, often at the point of deployment, but also for ongoing calibration of measurements from existing and new autonomous platforms. This includes biogeochemical observations for the nascent array of biogeochemical (BGC)-Argo floats; temperature and salinity for Deep Argo; and salinity for the core Argo array. GO-SHIP provides the relevant suite of global, full depth, high quality observations and co-located deployment opportunities that, for the foreseeable future, remain crucial to maintenance and evolution of Argo’s unique contribution to climate science. The evolution of GO-SHIP from a program primarily focused on physical climate to increased emphasis on ocean health and sustainability, in support of UN Sustainable Development Goal 14, has put an emphasis on the addition of essential ocean variables (EOVs) for biology and ecosystems in the program measurement suite. In conjunction with novel automated measurement systems, ocean color, particulate matter, and phytoplankton enumeration are being explored as GO-SHIP variables. The addition of biological and ecosystem measurements will enable GO-SHIP to determine trends and variability in these key indicators of ocean health. The active and adaptive GO-SHIP community has sustained the network, quality and relevance of the global repeat hydrography effort through societally important scientific results, increased exposure, and interoperability with new efforts and opportunities within the community.
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