Anastasia Falina

Mean full-depth summer circulation and transports at the northern periphery of the Atlantic Ocean in the 2000s

A mean state of the full-depth summer circulation in the Atlantic Ocean in the region in between Cape Farewell (Greenland), Scotland and the Greenland-Scotland Ridge (GSR) is assessed by combining 2002–2008 yearly hydrographic measurements at 59.5°N, mean dynamic topography, satellite altimetry data and available estimates of the Atlantic–Nordic Seas exchange. The mean absolute transports by the upper-ocean, mid-depth and deep currents and the Meridional Overturning Circulation (MOCσ = 16.5 ± 2.2 Sv, at σ0 = 27.55) at 59.5°N are quantified in the density space. Inter-basin and diapycnal volume fluxes in between the 59.5°N section and the GSR are then estimated from a box model. The dominant components of the meridional exchange across 59.5°N are the North Atlantic Current (NAC, 15.5 ± 0.8 Sv, σ0 27.55) east of the Reykjanes Ridge, the northward Irminger Current (IC, 12.0 ± 3.0 Sv) and southward Western Boundary Current (WBC, 32.1 ± 5.9 Sv) in the Irminger Sea and the deep water export from the northern Iceland Basin (3.7 ± 0.8 Sv, σ0 27.80). About 60% (12.7 ± 1.4 Sv) of waters carried in the MOCσ upper limb (σ0 27.55) by the NAC/IC across 59.5°N (21.1 ± 1.0 Sv) recirculates westward south of the GSR and feeds the WBC. 80% (10.2 ± 1.7 Sv) of the recirculating NAC/IC-derived upper-ocean waters gains density of σ0 27.55 and contributes to the MOCσ lower limb. Accordingly, the contribution of light-to-dense water conversion south of the GSR (∼10 Sv) to the MOCσ lower limb at 59.5°N is one and a half times larger than the contribution of dense water production in the Nordic Seas (∼6 Sv).

Recent changes in the Greenland–Scotland overflow‐derived water transport inferred from hydrographic observations in the southern Irminger Sea

Recent decadal changes (1955–2007) in the baroclinic transport (TBC) of the Deep Western Boundary Current (DWBC) carrying the Greenland–Scotland overflow-derived waters along the East Greenland slope are quantified from a set of hydrographic sections in vicinity of Cape Farewell. The updated historical record of TBC shows clear decadal variability (±2–2.5 Sv) with the transport minima in the 1950s and mid-1990s, maximum in the early 1980s and moderate-to-high transport in the 2000s. Since the mid-1990s, the DWBC TBC has increased by �2 Sv (significant at the 99.9% level), which constitute �20% of the mean absolute transport (9.0 Sv) as obtained from three cruises in 2002–2006. The DWBC TBC anomalies negatively correlate (R = –0.80) with thickness anomalies of the Labrador Sea Water (LSW) at its origin implying a close association, albeit not necessarily causative, between the DWBC transport east of Greenland and the LSW production.

On the Cascading of Dense Shelf Waters in the Irminger Sea

AbstractHydrographic data collected in the Irminger Sea in the 1990s–2000s indicate that dense shelf waters carried by the East Greenland Current south of the Denmark Strait intermittently descend (cascade) down the continental slope and merge with the deep waters originating from the Nordic Seas overflows. Repeat measurements on the East Greenland shelf at ~200 km south of the Denmark Strait (65°–66°N) reveal that East Greenland shelf waters in the Irminger Sea are occasionally as dense (σ0 > 27.80) as the overflow-derived deep waters carried by the Deep Western Boundary Current (DWBC). Clear hydrographic traces of upstream cascading of dense shelf waters are found over the continental slope at 64.3°N, where the densest plumes (σ0 > 27.80) originating from the shelf are identified as distinct low-salinity anomalies in the DWBC. Downstream observations suggest that dense fresh waters descending from the shelf in the northern Irminger Sea can be distinguished in the DWBC up to the latitude of Cape Farewell...

Assessing decadal changes in the Deep Western Boundary Current absolute transport southeast of Cape Farewell, Greenland, from hydrography and altimetry

[1] In earlier studies, the decadal variability of the Deep Western Boundary Current (DWBC) transport in the vicinity of Cape Farewell, Greenland, has been assessed from changes in the baroclinic velocities computed from hydrographic data and referenced to 1000 m depth. The main limitation of using such an estimate as an index for the DWBC absolute transport variability comes from the unaccounted for decadal velocity changes at the reference level (1000 m). These changes may substantially contribute to the DWBC absolute transport variability by compensating for or adding to the baroclinic transport changes. To assess this contribution to variability, we quantify the decadal velocity changes which occurred at 1000 m depth southeast of Cape Farewell since the mid-1990s. The analysis combines estimates of the baroclinic velocity changes in the water column derived from repeat hydrography at similar to 59.5 degrees N and the velocity changes at the sea surface derived from altimetry. An increase in the southward velocity at 1000 m above the DWBC between the periods of 1994-1997 and 2000-2007 is inferred. It indicates that the increase in the DWBC absolute transport was larger than the 2 Sv (1 Sv = 10(6) m(3) s(-1)) increase in its baroclinic component referenced to 1000 m. This result and the observed coherence of the DWBC absolute and baroclinic transport changes between individual observations imply that the DWBC absolute transport variability in the region is underestimated but qualitatively well represented by its baroclinic component on decadal and shorter time scales.

Cessation and partial reversal of deep water freshening in the northern North Atlantic: observation-based estimates and attribution

Abstract Recent decadal salinity changes in the Greenland-Scotland overflow-derived deep waters are quantified using CTD data from repeated hydrographic sections in the Irminger Sea. The Denmark Strait OverflowWater salinity record shows the absence of any net change over the 1980s–2000s; changes in the Iceland—Scotland Overflow Water (ISOW) and in the deep water column (σ0 > 27.82), enclosing both overflows, show a distinct freshening reversal in the early 2000s. The observed freshening reversal is a lagged consequence of the persistent ISOW salinification that occurred upstream, in the Iceland Basin, after 1996 in response to salinification of the northeast Atlantic waters entrained into the overflow. The entrainment salinity increase is explained by the earlier documented North Atlantic Oscillation (NAO)-induced contraction of the subpolar gyre and corresponding northwestward advance of subtropical waters that followed the NAO decline in the mid-1990s and continued through the mid-2000s. Remarkably, the ISOW freshening reversal is not associated with changes in the overflow water salinity. This suggests that changes in the NAO-dependent relative contributions of subpolar and subtropical waters to the entrainment south of the Iceland—Scotland Ridge may dominate over changes in the Nordic Seas freshwater balance with respect to their effect on the ISOW salinity.

Observed basin-wide propagation of Mediterranean water in the Black Sea

Mediterranean water entering the Black Sea through the Bosphorus Strait forms middepth intrusions that contribute to the salt, heat, and volume balances of the sea, ventilate its water column at intermediate depths and restrain the upward flux of hydrogen sulfide from deeper layers. Despite the importance for the Black Sea environment, the circulation of Mediterranean-origin water in the basin is fundamentally underexplored. Here we use hydrographic data collected from ships and Argo profiling floats to identify pathways of the Mediterranean intrusions in the general circulation system of the sea. While earlier the intrusions were observed primarily near the Bosphorus Strait, we present an evidence for their intermittent extensive propagation throughout the basin. We find that the main conduit for the intrusions is the southern limb of the Rim Current that carries the intruded water from the Bosphorus Strait eastward. A part of this eastward flow recirculates cyclonically into the interior of the sea, where traces of the intrusions gradually disappear because of mixing. We put forward the hypothesis that the formation of the most prominent intrusions is associated with strong cyclonic storms over the Bosphorus Strait, which lead to abnormally large influx of Mediterranean water.

Russian field studies of water exchange between the Atlantic and Arctic oceans in 2011

In May 2011, during cruise 32 of the R/V Akademik Sergey Vavilov, the observations were conducted over two sections: in the Faroe–Shetland Channel (section 1 in the figure) and over the section between Iceland and the Faroe Islands (section 2 in the figure). Each of the sections was occupied twice. A total of 72 stations were occupied: 33 in the Faroe–Shetland Channel and 39 over the Iceland–Faroe Ridge. During the expedition, 709 water samples were taken from Niskin bottles, and the concentrations of oxygen, silicates, and phos phates were determined in 810, 814, and 817 water samples, respectively.

On the renewal of Labrador Sea Water in the Irminger Basin

New evidence of Labrador Sea Water renewal as a result of deep convection in the Irminger Basin is obtained on the basis of the analysis of the data of the distribution of the dissolved oxygen concentration over six sections in the Subpolar North Atlantic in March–October of 1997.