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  1. Abstract The warm-to-cold densification of Atlantic Water (AW) around the perimeter of the Nordic Seas is a critical component of the Atlantic Meridional Overturning Circulation (AMOC). However, it remains unclear how ongoing changes in air-sea heat flux impact this transformation. Here we use observational data, and a one-dimensional mixing model following the flow, to investigate the role of air-sea heat flux on the cooling of AW. We focus on the Norwegian Atlantic Slope Current (NwASC) and Front Current (NwAFC), where the primary transformation of AW occurs. We find that air-sea heat flux accounts almost entirely for the net cooling of AW along the NwAFC, while oceanic lateral heat transfer appears to dominate the temperature change along the NwASC. Such differing impacts of air-sea interaction, which explain the contrasting long-term changes in the net cooling along two AW branches since the 1990s, need to be considered when understanding the AMOC variability. 
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    Free, publicly-accessible full text available December 1, 2024
  2. Abstract

    We present the first continuous mooring records of the West Greenland Coastal Current (WGCC), a conduit of fresh, buoyant outflow from the Arctic Ocean and the Greenland Ice Sheet. Nearly two years of temperature, salinity, and velocity data from 2018 to 2020 demonstrate that the WGCC on the southwest Greenland shelf is a well-formed current distinct from the shelfbreak jet but exhibits strong chaotic variability in its lateral position on the shelf, ranging from the coastline to the shelf break (50 km offshore). We calculate the WGCC volume and freshwater transports during the 35% of the time when the mooring array fully bracketed the current. During these periods, the WGCC remains as strong (0.83 ± 0.02 Sverdrups; 1 Sv ≡ 106m3s−1) as the East Greenland Coastal Current (EGCC) on the southeast Greenland shelf (0.86 ± 0.05 Sv) but is saltier than the EGCC and thus transports less liquid freshwater (30 × 10−3Sv in the WGCC vs 42 × 10−3Sv in the EGCC). These results indicate that a significant portion of the liquid freshwater in the EGCC is diverted from the coastal current as it rounds Cape Farewell. We interpret the dominant spatial variability of the WGCC as an adjustment to upwelling-favorable wind forcing on the West Greenland shelf and a separation from the coastal bathymetric gradient. An analysis of the winds near southern Greenland supports this interpretation, with nonlocal winds on the southeast Greenland shelf impacting the WGCC volume transport more strongly than local winds over the southwest Greenland shelf.

     
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  3. Free, publicly-accessible full text available August 1, 2024
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  5. Free, publicly-accessible full text available December 1, 2024
  6. Abstract

    Arctic‐origin and Greenland meltwaters circulate cyclonically in the boundary current system encircling the Labrador Sea. The ability of this freshwater to penetrate the interior basin has important consequences for dense water formation and the lower limb of the Atlantic Meridional Overturning Circulation. However, the precise mechanisms by which the freshwater is transported offshore, and the magnitude of this flux, remain uncertain. Here, we investigate wind‐driven upwelling northwest of Cape Farewell using 4 years of high‐resolution data from the Overturning in the Subpolar North Atlantic Program west Greenland mooring array, deployed from September 2014–2018, along with Argo, shipboard, and atmospheric reanalysis data. A total of 49 upwelling events were identified corresponding to enhanced northwesterly winds, followed by reduced along‐stream flow of the boundary current and anomalously dense water present on the outer shelf. The events occur during the development stage of forward Greenland tip jets. During the storms, a cross‐stream Ekman cell develops that transports freshwater offshore in the surface layer and warm, saline, Atlantic‐origin waters onshore at depth. The net fluxes of heat and freshwater for a representative storm are computed. Using a one‐dimensional mixing model, it is shown that the freshwater input resulting from the locus of winter storms could significantly limit the wintertime development of the mixed layer and hence the production of Labrador Sea Water in the southeastern part of the basin.

     
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  7. The most famous ocean current, the Gulf Stream, is part of a large system of currents that brings warm water from Florida to Europe. It is a main reason for northwestern Europe’s mild climate. What happens to the warm water that flows northward, since it cannot just pile up? It turns out that the characteristics of the water change: in winter, the ocean warms the cold air above it, and the water becomes colder. Cold seawater, which is heavier than warm seawater, sinks down to greater depths. But what happens to the cold water that disappears from the surface? While on a research ship, we discovered a new ocean current that solves this riddle. The current brings the cold water to an underwater mountain ridge. The water spills over the ridge as an underwater waterfall before it continues its journey, deep in the ocean, back toward the equator. 
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  8. Abstract

    Barrow Canyon in the northeast Chukchi Sea is a critical choke point where Pacific‐origin water, heat, and nutrients enter the interior Arctic. While the flow through the canyon has been monitored for more than 20 years, questions remain regarding the dynamics by which the Pacific‐origin water is fluxed offshore, as well as what drives the variability. In 2018, two high‐resolution shipboard surveys of the canyon were carried out—one in summer and one in fall—to investigate the water mass distribution and velocity structure of the outflow. During the summer survey, high percentages of Pacific water (summer water + winter water) were present seaward of the canyon, associated with strong northward outflow from the canyon and a well‐developed westward‐flowing Chukchi Slope Current (CSC). By contrast, high percentages of Pacific water were confined to the canyon proper and outer Chukchi shelf during the late‐fall survey, at which time the canyon outflow and CSC were considerably weaker. These differences can be attributed to differences in wind forcing during the time period of two surveys. A cyclone‐like circulation was present in the canyon during both surveys, which was also evident in the satellite‐derived sea surface height anomaly field. We argue that this feature corresponds to an arrested topographic Rossby wave, generated as the outflow responds to the deepening bathymetry of the canyon. By applying a self‐organizing map analysis using the satellite altimeter data from 2001 to 2020, we demonstrate that such a cyclone‐like structure is a prevailing aspect of the canyon outflow.

     
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