The Atlantic meridional overturning circulation (AMOC) is expected to decline dramatically over the 21st century, with severe impacts for Northern Hemisphere climate. After 20 years of sustained monitoring in the subtropics, a detectable AMOC weakening trend is now beginning to emerge. However, continuous observations at subpolar latitudes are currently too short-lived to determine any weakening signal above the large-amplitude interannual variability. Here, we introduce a new subpolar observing configuration, SCOTIA (Scotland-Canada overturning array), combining parts of the existing OSNAP mooring array with scattered CTD and Argo data, to extend the record of subpolar AMOC backward in time to cover the subtropical monitoring period, 2004-2024. SCOTIA facilitates a rigorous comparison of the decadal-scale variability in transports and overturning at subpolar and subtropical latitudes. Our results show subpolar AMOC varies on pentadal to decadal timescales with an amplitude comparable to that observed in the subtropics. Anomalously high overturning during 2016-2020 was driven by increased southward transports in the density classes associated with Labrador Sea Water. We find no statistically significant trend in subpolar AMOC during the period 2004-2024.

The Rockall Trough, northwest of Scotland and Ireland, is a key conduit for the North Atlantic Current (NAC) and European Slope Current (ESC) transporting heat and salt toward the Nordic Seas and Arctic Ocean while mediating exchanges between the open ocean and the European shelf. We present a decade-long record of Rockall Trough circulation from the Ellett Array providing the first continuous estimates of heat and freshwater transport between 2014 and 2024. We develop a methodology that combines the high spatial resolution of gliders with the high temporal resolution of moorings and ocean reanalysis output producing continuous eastern boundary velocity fields of the ESC for integration into the full Rockall Trough transport product. This approach improves the mean structure of the ESC, capturing the southward undercurrent previously unresolved and enhancing the ability to reproduce extreme, likely mesoscale, transport events. The Rockall Trough transport is dominated by the NAC flowing through the mid basin, exhibiting multi-year variability consistent with changes in the subpolar gyre and the mid-2010s cold freshwater anomaly. The ESC acts as a secondary driver, is not correlated with the NAC and is influenced by along-slope wind stress. Since 2022, warmer and saltier conditions, amplified by the 2023 extreme North Atlantic marine heatwave, have strengthened northward volume, heat, and salt transport through the Ellett Array. Our results highlight the value of sustained glider-based boundary current observations for Atlantic climate monitoring and demonstrate that the combined mooring-glider framework provides a robust and transferable approach for long-term ocean transport monitoring.

The North Atlantic Current (NAC) is a major source of heat toward the subpolar gyre and northern seas. However, its variability and drivers are not well understood. Here, we evaluated 8 years of continuous daily measurements as part of the international program Overturning in the Subpolar North Atlantic Program to investigate the NAC in the Iceland Basin. We found that the NAC volume and freshwater anomaly transport and heat content (HC) were highly variable with significant variability at timescales of 16–120 days to annual. Intraseasonal to short interannual variability was associated with mesoscale and intermittent mesoscale features abundant in the region. Composites analysis revealed that strong NAC periods were associated with less eddy kinetic energy in the Iceland Basin, which was consistent with the presence of frontal‐like structures instead of eddy‐like structures. On longer timescales, the westward migration of the eastern boundary of the subpolar North Atlantic (SPNA) gyre favors a stronger NAC volume transport and HC in the region. Stronger zonal wind stress triggers a fast response that piles water up between the SPNA and subtropical gyres, which increases the sea surface height gradient and drives the acceleration of the NAC. The strengthening of the NAC increases the heat and salt transport northward. During our study period, both heat and salt increased across the moorings. These observations are important for understanding the heat and freshwater variability in the SPNA, which ultimately impacts the Atlantic meridional overturning circulation.

The effect of wind-induced vertical velocity on the meridional coherence of Atlantic meridional overtuning circulation (AMOC) is examined using theory, observations, and a numerical model. Two cases are considered: (a) the AMOC computed in depth coordinates and (b) the AMOC computed in isopycnal coordinates. In depth space, the difference between the AMOC at different latitudes is largely explained by vertical transport across the 1000m $1000\,\mathrm{m}$ depth surface induced by Ekman pumping. In density space, this difference is explained by Ekman-driven heave of the neutral surface separating the upper and lower limbs. This adiabatic "sloshing" changes the relative volumes of the upper and lower AMOC limbs, obscuring the distribution and advection of the diapycnal transports which characterize the AMOC.

Variability of the Atlantic Meridional Overturning Circulation (MOC) has drawn extensive attention due to its impact on the global redistribution of heat and freshwater. Here we present the latest time series (2014-2022) of the Overturning in the Subpolar North Atlantic Program and characterize MOC interannual variability. We find that any single boundary current captures similar to 30% of subpolar MOC interannual variability. However, to fully resolve MOC variability, a wide swath across the eastern subpolar basin is needed; in the Labrador Sea both boundaries are needed. Through a volume budget analysis for the subpolar basins' lower limbs, we estimate the magnitude of unresolved processes (e.g., diapycnal mixing) required to close the mean budget (similar to 2 Sv). We find that in the eastern subpolar basin surface-forced transformation variability is linked to lower limb volume variability, which translates to MOC changes within the same year. In contrast, this linkage is weak in the Labrador Sea.

Abstract. Atlantic meridional overturning circulation has a notable seasonal component. This influences the jet stream and the location, frequency and intensity of extreme weather events. Understanding this seasonality is important for mitigating the impacts of AMOC changes on European weather and climate. Here we place meridional overturning and fluxes in a coherent framework. This framework highlights the integral relationship between meridional overturning circulation and property transports, both being functions purely of the overturning streamfunction Ψ. Using this framework we examine the seasonality observed in overturning and density, temperature and freshwater fluxes at the OSNAP line in the subpolar North Atlantic. We find the seasonal cycle of the MOC metric (the standard measure of overturning defined as the maximum of the overturning streamfunction) to be dominated by Ekman transports and the large-scale seasonal cycle of surface density; heat flux to be dominated by barotropic velocity variability; the seasonal cycle of freshwater flux by a combination of barotropic velocities and the salinity in the western boundary current; and density flux to reflect a broad range of characteristics and processes. We show that the MOC metric is a poor predictor, on seasonal time-scales, of either density fluxes or the more societally relevant ocean heat and freshwater transports. This is due to each of these metrics responding to different physical processes. The MOC metric, on seasonal timescales at least, has very high sensitivity to near-surface physical characteristics in a limited geographical area. These characteristics are not necessarily reflective of the fundamental processes driving overturning. Therefore, we suggest caution in the use of the standard MOC metric when studying overturning, and the routine use of the density flux as a valuable additional overturning metric.

The Atlantic meridional overturning circulation (AMOC) has a notable seasonal component. This influences the jet stream and the location, frequency, and intensity of extreme weather events. Understanding this seasonality is important for mitigating the impacts of AMOC changes on European weather and climate. Here, we place meridional overturning and fluxes in a coherent framework. This framework highlights the integral relationship between meridional overturning circulation and property transports, both being functions purely of the overturning streamfunction Psi. Using this framework, we examine the seasonality observed in overturning and density, temperature, and freshwater fluxes at the Overturning in the Subpolar North Atlantic Program (OSNAP) line in the subpolar North Atlantic. We find the seasonal cycle of the MOC metric (the standard measure of overturning, defined as the maximum of the overturning streamfunction) to be dominated by Ekman transports and the large-scale seasonal cycle of surface density; heat flux to be dominated by barotropic velocity variability; the seasonal cycle of freshwater flux to be dominated by a combination of barotropic velocities and the salinity in the western boundary current; and density flux to reflect a broad range of characteristics and processes. We show that the MOC metric is a poor predictor, on seasonal timescales, of either density fluxes or the more societally relevant ocean heat and freshwater transports. This is due to each of these metrics responding to different physical processes. The MOC metric, on seasonal timescales at least, has very high sensitivity to near-surface physical characteristics in a limited geographical area. These characteristics are not necessarily reflective of the fundamental processes driving overturning. Therefore, we suggest caution in the use of the standard MOC metric when studying overturning and the routine use of the density flux as a valuable additional overturning metric.

The Atlantic meridional overturning circulation (MOC) is traditionally monitored in terms of zonally integrated transport either in depth space or in density space. While this view has the advantage of simplicity, it obscures the rich and complex three-dimensional structure, so that the exact physics of the downwelling and upwelling branch remains poorly understood. The near-equivalence of the depth- and density-space MOC in the subtropics suggests that vertical and diapycnal volumes transports are intimately coupled, whereas the divergence of these two metrics at higher latitudes indicates that any such coupling is neither instantaneous nor local. Previous work has characterized the surface buoyancy forcing and mixing processes which drive diapycnal volume transport. Here, we develop a new analytical decomposition of vertical volume transport based on the vorticity budget. We show that most terms can be estimated from observations and provide additional insights from a high-resolution numerical simulation of the North Atlantic. Our analysis highlights the roles of 1) relative vorticity advection for the sinking of overflow fl ow water at the northern subpolar North Atlantic boundaries and 2) the geostrophic (3 effect for the sinking of dense waters in the intergyre region. These results provide insights into the coupling between density- and depth-space overturning circulations.

The eastern subpolar North Atlantic is a source of nutrients to the Northwest European Shelf and Arctic; however, biogeochemical transports in this important region are unknown. We examine variability in nutrients and carbon at the eastern boundary of the subpolar North Atlantic between 2017 and 2020, and calculate their transport by a branch of the North Atlantic Current and the European Slope Current. By combining observations from moorings and ship-based surveys, we derive novel biogeochemical property transports at high temporal resolution. Data from 63 m provide new evidence of a strong seasonal signal with silicate declining between April and May (-2.3 mu mol kg-1) and a concurrent increase in pH (0.04) and oxygen saturation (3.5%). Additionally, pH and oxygen saturation show a secondary peak in October during the autumn bloom. Biogeochemical transports are northwards and highly variable with volume transport dominating the variability over a multi-annual timescale. However, historical data suggests that nitrate and phosphate transports were 15% and 19% lower respectively in the late 2000s when the subpolar gyre circulation was weaker and lower nutrient source waters were dominant. These changes may have been amplified by concurrent reductions in volume transport. Changes in carbon and nutrient transports in the eastern subpolar North Atlantic may propagate downstream with potential effects on the Northwest European Shelf and Eurasian Arctic. Water flowing northward in the eastern subpolar North Atlantic transports nutrients onto the Northwest European Shelf and to the Arctic Ocean. However, biogeochemical transports through the region remain unknown. We examine variability in nutrients and carbon at the eastern boundary of the subpolar North Atlantic and calculate their transport by two important northward flowing currents. We use observations from ship-based surveys and instruments that recorded conditions in the ocean over 3 years to derive biogeochemical transports every 12 hr between May 2017 and October 2020. Transports of nutrients and carbon in the eastern subpolar North Atlantic are northwards although the transport is highly variable. Historical data suggests that when circulation around the subpolar North Atlantic is weaker, nutrient transports are around 15%-20% lower due to changes in the water nutrient concentrations. These changes may be amplified by concurrent reductions in current strength and volume transport. Changes in carbon and nutrient transports in the eastern subpolar North Atlantic may propagate downstream with potential effects on the Northwest European Shelf and Arctic Ocean. Silicate decreases and pH and oxygen increase from April to May with oxygen and pH showing a secondary peak in October Nutrient and carbon transports through the eastern boundary of the subpolar North Atlantic are northward and highly variable Biogeochemical transport magnitude may vary on multi-annual timescales and have downstream impacts

The Atlantic Meridional Overturning Circulation (AMOC) transports heat and salt between the tropical Atlantic and Arctic oceans. The interior of the North Atlantic subpolar gyre (SPG) is responsible for the much of the water mass transformation in the AMOC, and the export of this water to intensified boundary currents is crucial for projecting air–sea interaction onto the strength of the AMOC. However, the magnitude and location of exchange between the SPG and the boundary remains unclear. We present a novel climatology of the SPG boundary using quality-controlled CTD (conductivity–temperature–depth) and Argo hydrography, defining the SPG interior as the oceanic region bounded by 47∘ N and the 1000 m isobath. From this hydrography we find geostrophic flow out of the SPG around much of the boundary with minimal seasonality. The horizontal density gradient is reversed around western Greenland, where the geostrophic flow is into the SPG. Surface Ekman forcing drives net flow out of the SPG in all seasons with pronounced seasonality, varying between 2.45 ± 0.73 Sv in the summer and 7.70 ± 2.90 Sv in the winter. We estimate heat advected into the SPG to be between 0.14 ± 0.05 PW in the winter and 0.23 ± 0.05 PW in the spring, and freshwater advected out of the SPG to be between 0.07 ± 0.02 Sv in the summer and 0.15 ± 0.02 Sv in the autumn. These estimates approximately balance the surface heat and freshwater fluxes over the SPG domain. Overturning in the SPG varies seasonally, with a minimum of 6.20 ± 1.40 Sv in the autumn and a maximum of 10.17 ± 1.91 Sv in the spring, with surface Ekman the most likely mediator of this variability. The density of maximum overturning is at 27.30 kg m−3, with a second, smaller maximum at 27.54 kg m−3. Upper waters (σ0<27.30 kg m−3) are transformed in the interior then exported as either intermediate water (27.30–27.54 kg m−3) in the North Atlantic Current (NAC) or as dense water (σ0>27.54 kg m−3) exiting to the south. Our results support the present consensus that the formation and pre-conditioning of Subpolar Mode Water in the north-eastern Atlantic is a key determinant of AMOC strength.

The Rockall Trough (RT) is a key pathway for warm and salty water flowing northward, a process which plays a key role in dictating the western European climate. The picture of the mean circulation and variability in the RT is still emerging, as the record of continuous transport observations has only recently been extended to eight years. Here, for the first time, we present the temporally extended record of RT volume, heat and freshwater transports. An important feature of the RT circulation is the European Slope Current (ESC) which is poorly constrained by ship-based, mooring, and satellite observations. To tackle this, we gathered around 150 glider transects over 2.5 years which capture the ESC velocity field in unprecedented detail. The data are sufficient to characterise both the mean state and the emergent seasonal variability of the ESC, and reveal the year-round presence of a southward countercurrent at depth. Variability in the strength and structure of this previously unstudied feature modulates net northward transport in the eastern boundary current system.We also utilise these observations for monitoring the basin-wide overturning circulation as part of the newly developed OSNAP_I transect. We will present the first results from that programme.

Cold-water corals (CWCs) thrive in areas with complex and rough topography favoring the development of highly diverse benthic communities. Several biotic and abiotic factors including organic matter supply, temperature, bottom roughness and currents are important drivers of ecosystem structure and functioning in deep-sea environments at different spatial and temporal scales. Little is known, however, how basin-scale changes in the ocean climate affect these drivers at local scales. Here, we use high-resolution implementations of the hydrodynamic model ROMS-AGRIF for estimating characteristic spatial and temporal scales of local hydrodynamics in response to variations of basin-scale currents imposed by distinct changes of the Atlantic Meridional Overturning Circulation (AMOC) in the past century. We focus on two CWC communities on the SE Rockall Bank slope and at Condor Seamount. We considered two contrasting AMOC states that were identified from the 1958-2009 hindcast of the 1/20 degrees resolution VIKING20 North Atlantic basin-scale ocean circulation model and used as boundary conditions for the high-resolution local area models. At SE Rockall Bank, variability of near-bottom currents in both regions was largely dominated by tidal dynamics, but strongly modified by AMOC induced basin-scale variations of water mass properties and bottom currents. During strong AMOC years, waters in the main CWC depth corridor (600-1200 m) were cooler and less saline but were dominated by stronger bottom currents when compared with conditions during weak AMOC years. At Condor Seamount, bottom currents were largely unaffected by AMOC related changes close to the summit at water depths < 400 m. Kinetic energy dissipation rates derived from the 3D near -bottom velocity field appeared to positively relate with the in-situ CWC distribution. Kinetic energy dissipation is therefore proposed as a mechanistic descriptor of CWC presence as it provides a more mechanistic view of hydrodynamics driving organic matter supply to filter and suspension-feeding communities.

Understanding the variability of the Atlantic Meridional Overturning Circulation is essential for better predictions of our changing climate. Here we present an updated time series (August 2014 to June 2020) from the Overturning in the Subpolar North Atlantic Program. The 6-year time series allows us to observe the seasonality of the subpolar overturning and meridional heat and freshwater transports. The overturning peaks in late spring and reaches a minimum in early winter, with a peak-to-trough range of 9.0 Sv. The overturning seasonal timing can be explained by winter transformation and the export of dense water, modulated by a seasonally varying Ekman transport. Furthermore, over 55% of the total meridional freshwater transport variability can be explained by its seasonality, largely owing to overturning dynamics. Our results provide the first observational analysis of seasonality in the subpolar North Atlantic overturning and highlight its important contribution to the total overturning variability observed to date.

&lt;p&gt;In the subtropics, the Atlantic meridional overturning circulation (MOC) has the same strength and variability whether measured in depth- or density-space. Two different continuity budgets must therefore be satisfied north of the subtropics, one via diapycnal volume transport and the other via downward volume transport. However, as water can get denser without getting deeper (and vice versa), it is unclear why the integrated effect of these processes, the MOC, should have the same strength and variability in both depth- and density-space, provided one integrates these terms sufficiently far south (e.g. to 26 &amp;#176;N). Previous work has investigated the surface buoyancy forcing and mixing processes which drive diapycnal volume transport. Here, we use a suite of observational products and new analyses in a vorticity framework to study the magnitude and distribution of the various terms responsible for vertical volume transport, and gain further insight by also evaluating these terms using VIKING20X model output. We conclude that bottom Ekman transport and advection curl around the boundaries of the subpolar gyre, particularly around Greenland, are dominant drivers of downward vertical transport and hence crucial for closing MOC streamlines in depth-space, with much of the variability also projecting onto the MOC in density-space. As these processes are &amp;#8220;spun-up&amp;#8221; by the sub-polar gyre yet project onto the overturning, our results offer new insights into the coupling between the overturning and gyre circulations.&lt;/p&gt;

The Rockall Trough (RT) accommodates the warmest and saltiest branch of the North Atlantic Current, which delivers water from the Gulf Stream into the marine environment around western Europe. In addition, the European Slope Current (ESC) carries warm water northward along the eastern boundary of the RT, and exchange between the ESC and the continental shelf is a dominant factor in determining the oceanographic conditions around the British Isles. However, the picture of the mean circulation and variability in the RT is still emerging, with a continuous observational campaign still in its relative infancy. The ESC, in particular, is poorly constrained by ship-based, mooring, and satellite observations. In this paper, we examine the RT circulation and volume transport using a temporally extended and spatially expanded observing network. Six years of continuous mooring occupation reveal that a large-amplitude, basin-scale freshening event, previously detected south of Iceland around 2015, impacted the RT around 2017. Geostrophic transport was greatly reduced during this period, driven by a concurrent subsurface temperature increase at the western boundary. The circulation regained strength during the latter part of the record. We gathered 110 glider transects over 22 months which capture the ESC velocity field in unprecedented detail. The data are sufficient to characterize both the mean state and the emergent seasonal variability of the ESC, and reveal the year-round presence of a southward countercurrent at depth. Variability in the strength and structure of this previously unstudied feature modulates net northward transport in the eastern boundary current system. Plain Language Summary The Rockall Trough (RT) is a key pathway for warm and salty water flowing northward, a process which plays a key role in dictating the western European climate. However, the amount of water flowing northward, and how it changes over time, is still rather uncertain. In particular, the narrow boundary current in the eastern RT has previously proven difficult to measure. In this paper, we use 6 years of continuous oceanographic observations in the RT to monitor the flow. We also used underwater robots, called gliders, to focus on the narrow current in the eastern boundary. The data gathered give the best description of the ocean currents in the region to date. The study period coincided with a period of profound change across the subpolar North Atlantic, with a strong freshwater signal detected in the RT around 2017. The glider observations give a detailed view of the narrow eastern boundary current and how it varies seasonally, and also revealed the presence of a southward-flowing current at depth.

Changes in the Atlantic Meridional Overturning Circulation, which have the potential to drive societally-important climate impacts, have traditionally been linked to the strength of deep water formation in the subpolar North Atlantic. Yet there is neither clear observational evidence nor agreement among models about how changes in deep water formation influence overturning. Here, we use data from a trans-basin mooring array (OSNAP-Overturning in the Subpolar North Atlantic Program) to show that winter convection during 2014-2018 in the interior basin had minimal impact on density changes in the deep western boundary currents in the subpolar basins. Contrary to previous modeling studies, we find no discernable relationship between western boundary changes and subpolar overturning variability over the observational time scales. Our results require a reconsideration of the notion of deep western boundary changes representing overturning characteristics, with implications for constraining the source of overturning variability within and downstream of the subpolar region. Western boundary current variability in the subpolar North Atlantic is thought to reflect interior convection changes and determine Atlantic Meridional Overturning Circulation variability. Here, the authors show with an extended OSNAP time series that neither linkage is robust due to the complex dynamics in the region.

Observations of the eastern subpolar North Atlantic in the 2010s show exceptional freshening and cooling of the upper ocean, peaking in 2016 with the lowest salinities recorded for 120 years. Published theories for the mechanisms driving the freshening include: reduced transport of saltier, warmer surface waters northwards from the subtropics associated with reduced meridional overturning; shifts in the pathways of fresher, cooler surface water from the Labrador Sea driven by changing patterns of wind stress; and the eastward expansion of the subpolar gyre. Using output from a high-resolution hindcast model simulation, we propose that the primary cause of the exceptional freshening and cooling is reduced surface heat loss in the Labrador Sea. Tracking virtual fluid particles in the model backwards from the eastern subpolar North Atlantic between 1990 and 2020 shows the major cause of the freshening and cooling to be an increased outflow of relatively fresh and cold surface waters from the Labrador Sea; with a minor contribution from reduced transport of warmer, saltier surface water northward from the subtropics. The cooling, but not the freshening, produced by these changing proportions of waters of subpolar and subtropical origin is mitigated by reduced along-track heat loss to the atmosphere in the North Atlantic Current. We analyse modelled boundary exchanges and water mass transformation in the Labrador Sea to show that since 2000, while inflows of lighter surface waters remain steady, the increasing output of these waters is due to reduced surface heat loss in the Labrador Sea beginning in the early 2000s. Tracking particles further upstream reveals that the primary source of the increased volume of lighter water transported out of the Labrador Sea is increased recirculation of water, and therefore longer residence times, in the upper 500–1000 m of the subpolar gyre.

S1. Quality control and gridding of profile data S2.Additional datasets S3.Seasonal anomalies in boundary hydrography S4.Diffusive heat flux S5.Sub-1000 m transport correction S6.Decomposition of heat and freshwater fluxes into overturning and along-isopycnal components S1.2 Density inversion testWe performed a simple density inversion test to identify and flag temperature and salinity profiles which resulted in density inversions.CT and SA profiles were binned onto a 20 dbar grid, and σ0 recalculated.The profile was scanned for density inversions.If an inversion of > 0.03 kgm -3 was detected, the whole profile was rejected (Fig. S1).

Circulation at the boundary of the subpolar North Atlantic influences both the horizontal (gyre) and vertical (overturning) components of the flow structure. While boundary current transport projects directly onto subpolar gyre strength, recent modelling studies have highlighted that buoyancy fluxes between the basin interior and the boundary, followed by rapid buoyancy export by boundary currents, are crucial steps in projecting air-sea interaction onto the strength of the Atlantic Meridional Overturning Circulation (AMOC). This work seeks observational insights into these key boundary processes.To achieve this, we have constructed a robust boundary climatology from quality controlled CTD and Argo hydrography since the turn of the millennium. Following the 1000 m isobath north of 47 °N and aggregating data into 100 km bins, we build a picture of the typical large-scale temperature and salinity structure for each month.This product will allow us to identify where and when important interior-boundary buoyancy fluxes take place over a seasonal cycle. A first step is to evaluate geostrophic flow into the boundary, and hence describe the vertical structure of advective buoyancy exchange. By appealing to satellite altimetry and Argo trajectories, we can also estimate turbulent eddy fluxes both at the surface and 1000 m depth. Models indicate these parameters are key in dictating the pathways for the AMOC lower limb, and we will place our observational findings in the context of these results.Boundary current strength is another key parameter dictating the export of dense water from the subpolar gyre. We will appeal to satellite altimetry to build corresponding climatologies for barotropic boundary flow. Furthermore, along-slope density gradients give rise to a baroclinic boundary current forcing term, which we aim to investigate here. Water density generally increases as we follow the gyre counter-clockwise, with the notable exception of the West Greenland Current section, and our product allows us to partition the spatially-varying contribution of temperature and salinity towards these density gradients. For example, we can evaluate the impact of cooling along the eastern boundary, or surface freshening around southern Greenland, on the dynamics of boundary flow. Ultimately, we would like to understand the evolution of the dynamical balance experienced by a hypothetical fluid parcel traversing the entire subpolar gyre.