Search for: All records

Bering Strait is the only ocean gateway connecting the Pacific and Arctic oceans. The ∼1 Sv northward flow of Pacific water through the strait to the Arctic Ocean has been increasing by ∼0.01 Sv/yr since 1990. Monthly dynamic ocean topography (DOT), wind, and sea‐ice data at Bering Strait are analyzed in context with the long‐term record of flow through the strait to investigate local drivers. Ocean transport is found to be proportional to the across‐strait slope in DOT, suggesting some component of the flow is in geostrophic balance. Along‐strait ocean surface stresses, which modulate the across‐strait DOT slope via Ekman transport, are analyzed in the presence of a seasonally varying ice cover. It is shown that northward interior ocean flow under sea ice in winter results in southward surface stresses, and westward Ekman transport that slows the geostrophic component of the northward ocean flow. As the number of open water days local to Bering Strait increase each year, we find no trend in the annual mean surface stress, that is, the loss of sea ice is not leading to increased northward wind stress input that would enhance northward ocean flow. This analysis is consistent with the theory that changes in both the atmosphere and ocean non‐local to Bering Strait are likely driving the increased transport from the Pacific into the Arctic via Bering Strait. 

The Central Arctic Ocean remains profoundly understudied, particularly with respect to carbon cycling, ecosystem alteration, and associated changes in atmospheric, ice and ocean physics that drive those biological and biogeochemical systems. The region is expected to experience continued marked changes over the coming decades, driven by ongoing climate warming. Yet, because of relatively limited understanding of fundamental characteristics and processes in the region, predicting these changes and their Pan-Arctic linkages remains difficult. The Synoptic Arctic Survey (SAS) is organized around three major research areas: (1) physical drivers of importance to the ecosystem and carbon cycle; (2) the ecosystem response and (3) the carbon cycle. The overarching questions are: “What is the present state, and what are the major ongoing transformations of the Arctic marine system?” The overall objective of this expedition was to quantify the present states of the physical, biological, and biogeochemical systems of the Pacific Arctic (here defined as the Chukchi Sea, Beaufort shelf/slope, Chukchi Borderlands) and Canadian Basin (i.e., the Makarov and Canada basins) during summer 2022. A key goal is to document temporal changes where possible by comparison with historical data and to quantify linkages among adjacent shelves, slopes, and deep basins on a Pan-Arctic scale. These objectives are part of the International Synoptic Arctic Survey (SAS; 2021-2022) that seeks Pan-Arctic understanding of core ocean variables on a quasi-synoptic, spatially distributed basis using coordinated, international efforts. The findings of this expedition, a US contribution to the SAS, will be a foundation and legacy for future, quasi-decadal assessments of rapid and evolving Arctic Ocean system change." - Cruise Report USCGC Healy HLY2202/AWS2022 [Prepared by Carin Ashjian (cashjian@whoi.edu) and the HLY2202 Science Team] This data set contains measurements of water properties such as temperature, conductivity, chlorophyll fluorescence, Photosynthetically Available Radiation (PAR), oxygen, beam attenuation, and beam transmission. These measurements were collected by a Seabird 9 conductivity, temperature, and depth (CTD) and associated sensors on a CTD rosette lowered from the ship at discrete stations during cruise HLY2202. 

Abstract The Canada Basin (CB) has seen significant sea‐ice loss in recent decades. We use output from the Pan‐Arctic Ice‐Ocean Modeling and Assimilation System to examine the 1979–2023 evolution of seasonal sea‐ice volume (SIV) changes in the CB partitioned into advective and thermodynamic changes. In winter, some years show net convergence into the region that is of comparable magnitude to the SIV change attributed to sea‐ice growth. In summer, melt/ablation dominates the change each year. In both seasons, 44 year trends in seasonal SIV changes are driven primarily by thermodynamic processes. The inferred thermodynamic growth each year is nearly equal to the inferred melt consistent with SIV at the end of the melt season declining more rapidly than SIV at the end of the growth season. Increased melt season atmospheric heating of the ice‐ocean system over 1979–2023, estimated from ERA5 reanalysis, is consistent with the ice‐albedo feedback. In the growth season, net cumulative atmospheric heat release from the ice‐ocean system shows no trend, suggesting increases in inferred thermodynamic ice growth can be attributed to more rapid growth of thinner ice. In each season, cumulative atmospheric heat input exceeds that required for ice melt/growth resulting in a residual that influences ocean heat content (OHC). Seasonal OHC changes, inferred from ocean observations, are equal to approximately one‐third of this residual, although limited ocean observations leave the total heat budget poorly constrained, highlighting a need for more water column observations. 

Abstract Analysis of dissolved oxygen (O₂) in the Arctic's surface ocean provides insights into gas transfer between the atmosphere‐ice‐ocean system, water mass dynamics, and biogeochemical processes. In the Arctic Ocean's Canada Basin mixed layer, higher O₂concentrations are generally observed under sea ice compared to open water regions. Annual cycles of O₂and O₂saturation, increasing from summer through spring and then sharply declining to late summer, are tightly linked to sea ice cover. The primary fluxes that influence seasonal variability of O₂are modeled and compared to Ice‐Tethered Profiler O₂observations to understand the relative role of each flux in the annual cycle. Findings suggest that sea ice melt/growth dominates seasonal variations in mixed layer O₂, with minor contributions from vertical entrainment and atmospheric exchange. While the influence of biological activity on O₂variability cannot be directly assessed, indirect evidence suggests relatively minor contributions, although with significant uncertainty. Past studies show that O₂molecules are expelled from sea ice during brine rejection; sea ice cover can then inhibit air‐sea gas exchange resulting in winter mixed layers that are super‐saturated. Decreasing mixed layer O₂concentrations and saturation levels are observed during winter months between 2007 and 2019 in the Canada Basin. Only a minor portion of the decreasing trend in wintertime O₂can be attributed to decreased solubility. This suggests the O₂decline may be linked to more efficient air‐sea exchange associated with increased open water areas in the winter sea ice pack that are not necessarily detectable via satellite observations. 

Abstract Analysis of dissolved oxygen (O₂) in the Arctic's surface ocean provides insights into gas transfer between the atmosphere‐ice‐ocean system, water mass dynamics, and biogeochemical processes. In the Arctic Ocean's Canada Basin mixed layer, higher O₂concentrations are generally observed under sea ice compared to open water regions. Annual cycles of O₂and O₂saturation, increasing from summer through spring and then sharply declining to late summer, are tightly linked to sea ice cover. The primary fluxes that influence seasonal variability of O₂are modeled and compared to Ice‐Tethered Profiler O₂observations to understand the relative role of each flux in the annual cycle. Findings suggest that sea ice melt/growth dominates seasonal variations in mixed layer O₂, with minor contributions from vertical entrainment and atmospheric exchange. While the influence of biological activity on O₂variability cannot be directly assessed, indirect evidence suggests relatively minor contributions, although with significant uncertainty. Past studies show that O₂molecules are expelled from sea ice during brine rejection; sea ice cover can then inhibit air‐sea gas exchange resulting in winter mixed layers that are super‐saturated. Decreasing mixed layer O₂concentrations and saturation levels are observed during winter months between 2007 and 2019 in the Canada Basin. Only a minor portion of the decreasing trend in wintertime O₂can be attributed to decreased solubility. This suggests the O₂decline may be linked to more efficient air‐sea exchange associated with increased open water areas in the winter sea ice pack that are not necessarily detectable via satellite observations. 

Abstract The freshwater content of the Arctic Ocean has increased dramatically in the last two decades, particularly in the Beaufort Gyre. However, quantifying the sources of this change is an observational challenge and has historically been limited by methodological differences across studies. Here we derive observation‐based freshwater budgets from volume and mass budgets for the Arctic Ocean and the Beaufort Gyre from 2003 to 2020. Our budgets include all sources and sinks (river runoff, precipitation minus evaporation, land ice melt, sea ice export, sea ice melt, and ocean fluxes) as well as volume and mass storage terms measured by satellite. We find that Arctic freshwater changes are dominated by changes in the Beaufort Gyre, and we reconcile this with previous studies that argue for freshwater compensation between the Beaufort Gyre and the rest of the Arctic. We use inverse methods to close the volume and mass budgets within observational uncertainty and link the observed Arctic freshwater changes to the sources and sinks. Our budget analysis demonstrates that small changes to the ocean fluxes (smaller than we can measure) can account for all freshwater storage changes in the Arctic, highlighting the need for more careful accounting and detailed ocean observations in this rapidly changing environment. 

The Arctic Ocean's Beaufort Gyre is a dominant feature of the Arctic system, a prominent indicator of climate change, and possibly a control factor for high-latitude climate. The state of knowledge of the wind-driven Beaufort Gyre is reviewed here, including its forcing, relationship to sea-ice cover, source waters, circulation, and energetics. Recent decades have seen pronounced change in all elements of the Beaufort Gyre system. Sea-ice losses have accompanied an intensification of the gyre circulation and increasing heat and freshwater content. Present understanding of these changes is evaluated, and time series of heat and freshwater content are updated to include the most recent observations.