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The flow around an obstacle can be visualized using relatively simple and cheap apparatus. Such an experiment is described here including photographs showing eddies.

[1] Greenland's tip jets are low-level, high wind speed jets forced by an interaction of the synoptic-scale atmospheric flow and the steep, high orography of Greenland. These jets are thought to play an important role in both preconditioning for, and triggering of, open-ocean convection in the Irminger Sea. However, the relatively small spatial scale of the jets prevents their accurate representation in the relatively low resolution (∼1 degree) atmospheric (re-)analyses which are typically used to force ocean general circulation models (e.g. ECMWF ERA-40 and NCEP reanalyses, or products based on these). Here we present a method of ‘bogussing’ Greenland's tip jets into such surface wind fields and thus, via bulk flux formulae, into the air-sea turbulent flux fields. In this way the full impact of these mesoscale tip jets can be incorporated in any ocean general circulation model of sufficient resolution. The tip jet parameterization is relatively simple, making use of observed linear gradients in wind speed along and across the jet, but is shown to be accurate to a few m s−1 on average. The inclusion of tip jets results in a large local increase in both the heat and momentum fluxes. When applied to a 1-dimensional mixed-layer model this results in a deepening of the winter mixed-layer of over 300 m. The parameterization scheme only requires 10 meter wind speed and mean sea level pressure as input fields; thus it is also suitable for incorporation into a coupled atmosphere-ocean climate model at the coupling stage.

[1] The Antarctic Slope Front presents a dynamical barrier between the cold Antarctic shelf waters in contact with ice shelves and the warmer subsurface waters offshore. Two hydrographic sections with full-depth current measurements were undertaken in January and February 2009 across the slope and shelf in the southeastern Weddell Sea. Southwestward surface-intensified currents of ∼30 cm s−1, and northeastward undercurrents of 6–9 cm s−1, were in thermal-wind balance with the sloping isopycnals across the front, which migrated offshore by 30 km in the time interval between the two sections. A mid-depth undercurrent on February 23 was associated with a 130-m uplift of the main pycnocline, bringing Warm Deep Water closer to the shelf break. This vertical displacement, comparable to that caused by seasonal variations in wind speed, implies that undercurrents may affect the exchanges between coastal and deep waters near the Antarctic continental margins.

The confluence between the Brazil Current and the Malvinas Current [the Brazil–Malvinas Confluence (BMC)] in the Argentine Basin is characterized by a complicated thermohaline structure favoring the exchanges of mass, heat, and salt between the subtropical gyre and the Antarctic Circumpolar Current (ACC). Analysis of thermohaline properties of hydrographic sections in the BMC reveals strong interactions between the ACC and subtropical fronts. In the Subantarctic Front, Subantarctic Mode Water (SAMW), Antarctic Intermediate Water (AAIW), and Circumpolar Deep Water (CDW) warm (become saltier) by 0.4° (0.08), 0.3° (0.02), and 0.6°C (0.1), respectively. In the subtropical gyre, AAIW and North Atlantic Deep Water have cooled (freshened) by 0.4° (0.07) and 0.7°C (0.11), respectively. To quantify those ACC–subtropical gyre interactions, a box inverse model surrounding the confluence is built. The model diagnoses a subduction of 16 ± 4 Sv (1 Sv ≡ 106 m3 s−1) of newly formed SAMW and AAIW under the subtropical gyre corresponding to about half of the total subduction rate of the South Atlantic found in previous studies. Cross-frontal heat (0.06 PW) and salt (2.4 × 1012 kg s−1) gains by the ACC in the BMC contribute to the meridional poleward heat and salt fluxes across the ACC. These estimates correspond to perhaps half of the total cross-ACC poleward heat flux. The authors’ results highlight the BMC as a key region in the subtropical–ACC exchanges.

Composite analysis is applied to study the dynamical ocean response to Madden-Julian (MJ) events, measured by anomalies in sea surface height from the merged TOPEX/Poseidon-European Remote Sensing satellite altimetry dataset. In each of the tropical ocean basins, significant equatorial waves are forced, which are shown to modulate the sea surface temperature (SST) by 0.2-0.3 degC in the absence of strong surface heat fluxes. In the Indian Ocean there is a clear dynamical response which may play a significant role in generating later MJ events. Surface westerly winds, associated with the active phase of the Madden-Julian Oscillation (MJO), force an eastward-propagating oceanic downwelling equatorial Kelvin wave, which, on reaching the eastern boundary at Sumatra, forces reflected downwelling equatorial Rossby waves and coastal Kelvin waves. The coastal Kelvin waves propagate southwards towards northern Australia and northwards into the Bay of Bengal, and will be important for local physical, chemical and biological processes. The equatorial Rossby waves propagate westward across the Indian Ocean, arriving in the western Indian Ocean approximately 80-100 days after the initial Kelvin wave was generated. The arrival of these waves generates positive SST anomalies which leads to convection and may trigger the next-but-one MJ event, or amplify the low-frequency tail of the MJO. This constitutes a coupled feedback mechanism from the ocean dynamics onto the MJO, somewhat similar to the delayed oscillator mechanism for the El Nino Southern Oscillation.

[1] The intricate near-circumpolar system of fronts and currents surrounding Antarctica isolates much of Earth's freshwater from the saline oceans immediately north. The Antarctic Slope Front sustains bathymetrically steered flow at the shelf break, whereas the shallow Coastal Current travels rapidly alongside the ice front. A hydrographic survey of the southeastern Weddell Sea finds these two features to have merged near the narrow (

Monitoring the sources and fate of freshwater in the East Greenland Current (EGC) is important, as this water has the potential to suppress deep convection in the Nordic and Labrador Seas if the outflow of freshwater from the Arctic Ocean increases in response to climate change. Here, hydrographic, oxygen isotope ratio and dissolved barium concentration sections across Denmark Strait collected in 1998 and 1999 are used to determine the freshwater composition of the EGC at these times. Comparison of meltwater fluxes at Denmark Strait and Fram Strait indicates a net melting of sea ice into the EGC between these two locations, with a significant proportion of sea ice drifting into the Nordic Seas or on to the East Greenland Shelf. We conclude that the phase of freshwater exiting the Arctic Ocean through Fram Strait is important in determining its possible impact on deep water formation in the Nordic and Labrador Seas.

The backscattered signal intensity from a shipborne RD Instruments 150 kHz Acoustic Doppler Current Profiler is compared with zooplankton abundance during surveys around the Indian Ocean island of Aldabra. Significant correlation is found between the range-corrected backscatter summed from the surface to a depth of 200 m and the biomass collected by a net haul over the same vertical range at the same station. Biomass is expressed as mg C m−3 and is obtained by using a modified displacement volume method. Unlike previous work by Flagg and Smith (1989, Deep-Sea Research, 36, 455–474; 1989, Proceedings of OCEAN '89, Marine Technology Society and I.E.E.E.) the ADCP was unmodified. This indicates that, until such modifications and calibrations as they suggest are carried out, data from existing instruments are still worth investigating. Problems involved in the determination of flow noise inherent in shipborne ADCP backscatter measurement are discussed. Care must be taken if backscatter is studied when the ship is steaming. Nevertheless the application of the ADCP to combined studies of flow fields and biological productivity offers promise of continuous along-track estimates of zooplankton biomass when supplemented by spot calibrations.

[1] Determining meridional heat flux in the Southern Ocean is critical to the accurate understanding and model simulation of the global ocean. Mesoscale eddies provide a significant but poorly-defined contribution to this transport. An eighteen-month deep-water current meter array deployment in Shag Rocks Passage (53°S, 48°W) between May 2003 and November 2004 provides estimates of the eddy flux of heat across the Polar Front. We calculate a statistically nonzero (99% level), vertically coherent local poleward heat flux of 12.0 ± 5.8 kW m−2 within the eddy frequency band at ∼2750 m depth. Exceeding previous deep-water estimates by up to an order of magnitude, this highlights the large spatial variation in flux estimates and illustrates that constriction of circumpolar fronts facilitates large eddy transfers of heat southwards.

[1] It has been speculated that low-level reverse tip-jets, caused by the interaction of synoptic-scale atmospheric flow and Greenland, are an important mechanism for forcing open ocean convection in the south-east Labrador Sea. Here float data and meteorological reanalysis fields from the winter of 1996/1997, in combination with a simple mixed-layer ocean model, are used to show that, although relatively deep ocean convection did occur during this winter, the primary forcing mechanism was cold-air outbreaks from the Labrador coast rather than the smaller scale reverse tip-jets. During this winter, the North Atlantic Oscillation (NAO) was in a weak positive phase. Similar treatments of the winters of 1994/1995 (strong, positive NAO) and 1995/1996 (strong, negative NAO) suggest that the result is robust regardless of the state of the NAO.

19 páginas, 10 figuras, 1 tabla., We present CTD and ADCP surveys around the Indian Ocean coral atolls of Aldabra (46°20′E, 9°25′S) and Cosmoledo (47°30E, 9°45′S) during April-July 1987. These isolated, steep-sided islands situated in deep (4000 m) water in the South Equatorial Current provide examples of flow disturbance which are compared to laboratory studies of eddy generation by a circular cylinder in a channel. For sufficiently strong and steady flows, a doming of the isopycnals is observed in the lee of the islands. The sea-surface temperature decreases and the salinity increases as cool, saline water is mixed from below. Just as in the case of islands in tidally dominated shelf seas, we observe an increase in the chlorophyll content of the water behind the island, indicative of enhanced phytoplankton productivity caused by the flow disturbance. This anomalous region may be associated with an eddy trapped downstream of the island. The incident flows were not strong enough to generate a vortex street of eddies spun off in a wake. When the incident flows are weak and fluctuating, no evidence for eddies is seen; and there is no doming of the isopycnals leading to low sea-surface temperature and high chlorophyll content., This project was supported by NERC grant GR3/5549.

The heat transported by the lower limb of the Southern Ocean meridional overturning circulation is commonly held to be negligible in comparison with that transported by eddies higher in the water column. We use output from one of the first global high resolution models to have a reasonably realistic export of Antarctic Bottom Water, the OCCAM one twelfth degree model. The heat fluxed southward by the deep overturning cell using the annual mean field for 1994 at 56S is 0.033 PW, but the 5-day mean fields give a larger heat flux (0.048 and 0.061 PW depending on calculation method). This is more than 30% of previous estimates of the total heat flux. Eddies and other transients add considerably to the heat flux. These results imply that this component of meridional heat flux may not be negligible as has been supposed.

The cavities beneath Antarctic ice shelves are among the least studied regions of the World Ocean, yet they are sites of globally important water mass transformations. Here we report results from a mission beneath Fimbul Ice Shelf of an autonomous underwater vehicle. The data reveal a spatially complex oceanographic environment, an ice base with widely varying roughness, and a cavity periodically exposed to water with a temperature significantly above the surface freezing point. The results of this, the briefest of glimpses of conditions in this extraordinary environment, are already reforming our view of the topographic and oceanographic conditions beneath ice shelves, holding out great promises for future missions from similar platforms.

A decomposition of meridional overturning circulation (MOC) cells into geostrophic vertical shears, Ekman, and bottom pressure–dependent (or external mode) circulation components is presented. The decomposition requires the following information: 1) a density profile wherever bathymetry changes to construct the vertical shears component, 2) the zonal-mean zonal wind stress for the Ekman component, and 3) the mean depth-independent velocity information over each isobath to construct the external mode. The decomposition is applied to the third-generation Hadley Centre Coupled Ocean–Atmosphere General Circulation Model (HadCM3) to determine the meridional variability of these individual components within the Atlantic Ocean. The external mode component is shown to be extremely important where western boundary currents impinge on topography, and also in the area of the overflows. The Sverdrup balance explains the shape of the external mode MOC component to first order, but the time variability of the external mode exhibits only a very weak dependence on the wind stress curl. Thus, the Sverdrup balance cannot be used to determine the external mode changes when examining temporal change in the MOC. The vertical shears component allows the time-mean and the time-variable upper North Atlantic MOC cell to be deduced at 25°S and 50°N. A stronger dependency on the external mode and Ekman components between 8° and 35°N and in the regions of the overflows means that hydrographic sections need to be supplemented by bottom pressure and wind stress information at these latitudes. At the decadal time scale, variability in Ekman transport is less important than that in geostrophic shears. In the Southern Hemisphere the vertical shears component is dominant at all time scales, suggesting that hydrographic sections alone may be suitable for deducing change in the MOC at these latitudes.

[1] The short-term response of the climate system to a freshwater anomaly in the Southern Ocean is investigated using a coupled global climate model. As a result of the anomaly, ventilation of deep waters around Antarctica is inhibited, causing a warming of the deep ocean, and a cooling of the surface. The surface cooling causes Antarctic sea-ice to thicken and increase in extent, and this leads to a cooling of Southern Hemisphere surface air temperature. The surface cooling increases over the first 5 years, then remains constant over the next 5 years. There is a more rapid response in the Pacific Ocean, which transmits a signal to the Northern Hemisphere, ultimately causing a shift to the negative phase of the North Atlantic Oscillation in years 5–10.

[1] Data from the Deep Ocean Ventilation Through Antarctic Intermediate Layers (DOVETAIL) and Antarctic Large-Scale Box Analysis and the Role of the Scotia Sea (ALBATROSS) projects are combined in the region of the Antarctic Peninsula and the South Scotia Ridge to determine the paths and transports associated with the Antarctic Coastal Current, the Antarctic Slope Front, and the Weddell Front. The Antarctic Coastal Current flows over the Antarctic continental shelf and is not tied to a particular isobath. It transports ∼1 Sv westward to the Bransfield Strait. Its subsequent course is uncertain, but we speculate that it may continue southwest along the western side of the Antarctic Peninsula, close to the coast. The Antarctic Slope Front, present almost all the way around Antarctica tied to the continental slope, has not previously been mapped after it reaches the tip of the Antarctic Peninsula. We show that the frontal jet splits into two branches in the northwest Powell Basin where the isobaths diverge. The shoreward portion of the water associated with the front (lying above isobaths shallower than 1500 m) is able to cross the South Scotia Ridge and head northwestward and retains many of the properties of the Antarctic Slope Front. It is associated with a transport of ∼7 Sv. The portion of the front constrained to lie above isobaths deeper than 1500 m becomes the Weddell Front. This takes a path around the northern Powell Basin and south of the South Orkney Islands. Of the ∼13 Sv that circulates around the southern flank of the South Orkney Plateau, ∼8 Sv of Weddell Sea Deep Water and Warm Deep Water leaves the front to continue west. The remaining shallow and intermediate water retroflects and returns south associated with the Weddell Front through the Orkney Passage. Approximately 5–7 Sv is transported eastward associated with the Weddell Front, tied closely to the southern flanks of the Bruce and Discovery Banks above the 2000–2500 m isobaths, and forming the southern boundary of the Weddell Scotia Confluence.

A particle tracking scheme that uses velocity output from an interannually varying forced run of a global ocean circulation model (Parallel Ocean Climate Model; POCM_4C) allows variability in the transport pathways across the Scotia Sea to South Georgia to be examined for the first time. The time-variant surface fluxes introduce realistic variability into the model velocity fields. This causes large variations in near-surface, mixed-layer transport from the Antarctic Peninsula region to South Georgia, an island in the southwest Atlantic sector of the Southern Ocean. The variability occurs on a variety of timescales with seasonal and longer periods of variability apparent in the 18 year time series of results. A quasi-four year period of variability is evident across the region in the sea surface temperature fields of POCM_4C and appears in the particle tracking results. This period, noted in other Southern Ocean data sets and ascribed to the Antarctic Circumpolar Wave, has been observed in the reproductive success of higher marine predators breeding on the island. The predicted oceanographic variability is likely to be significant for the South Georgia ecosystem by affecting the influx into the region of Antarctic krill (Euphausia superba), the main prey of the higher predators.

International audience; Hydrographic and lowered acoustic Doppler current profiler data along a line from the Falkland Islands to South Georgia via the Maurice Ewing Bank are used to estimate the flow of circumpolar water into the Argentine Basin, and to study the interaction of the Antarctic Circumpolar Current with the Falkland Plateau. The estimated net transport of 129 ± 21 Sv (Sv ≡ 106 m3 s−1) across the section is shared between three major current bands. One is associated with the Subantarctic Front (SAF; 52 ± 6 Sv), and the other two with branches of the Polar Front (PF) over the sill of the Falkland Plateau (44 ± 9 Sv) and in the northwestern Georgia Basin (45 ± 9 Sv). The latter includes a local reinforcement (∼20 Sv) by a deep anticyclonic recirculation around the Maurice Ewing Bank. While the classical hydrographic signature of the PF stands out in this eastbound branch, it is less distinguishable in the northbound branch over the plateau. Other circulation features are a southward entrainment of diluted North Atlantic Deep Water from the Argentine Basin over the eastern part of the Falkland Plateau, and an abyssal anticyclonic flow in the western Georgia Basin, opposite to what was generally assumed. The different behavior of the SAF and PF at the Falkland Plateau (no structural modification of the former and partitioning of the latter) is attributed to the PF being deeper than the sill depth on the upstream side of the plateau, unlike the SAF. It is suggested that the partitioning takes place at a location where the 2500-m and 3000-m isobaths diverge at the southern edge of the plateau. The western branch of the PF crosses the plateau at a distance of ∼250 km to the east of the SAF. Comparison with a section across the Falkland Current farther downstream shows that its deep part subsequently joins the SAF on the northern side of the plateau where the 2000–3000 m isobaths converge in the steep Falkland Escarpment. The result of this two-stage bathymetric effect is a net transfer of at least 10 Sv from the PF to the SAF at the crossing of the Falkland Plateau.

Two meridional hydrographic transects (in 1995 and 1999) across the eastern Scotia Sea are used to investigate variability in the deep and bottom waters between the South Scotia Ridge and South Georgia. There is a significant warming of the warm deep water (WDW) south of the southern boundary of the Antarctic Circumpolar Current (ACC); waters are approximately 0.1°–0.2°C warmer in 1999 than 1995. This is due mainly to raised WDW potential temperatures in the Weddell Sea being fed through to the Scotia Sea as the WDW flows northeastward in the Weddell Gyre. There is a warming of the Weddell Sea Deep Water (WSDW) of approximately 0.05°C across the whole extent of the section, and an accompanying change in salinity that maintains the potential temperature–salinity relationship. This is caused by variability in the properties of the water overflowing the South Scotia Ridge, rather than enhanced outflow of the bottom layer of the Scotia Sea or movements of the ACC fronts, and may be related to changes in the intensity of the Weddell Gyre circulation. Consideration of other works suggests that the colder WSDW of 1995 is likely to be the anomalous case, rather than the warmer WSDW of 1999. The 1999 section reveals an inflow of Lower WSDW from east of the South Sandwich Arc via the Georgia Passage; this is constrained to the south of the southern boundary, and is not apparent in the 1995 measurements. Meanders in the southern boundary at Georgia Passage are likely to play a role in controlling the inflow of Lower WSDW, although changes in the peak density of the WSDW flowing across the South Scotia Ridge may be important also, with a denser inflow from the south acting to preclude an inflow of similar density from the northeast.

12 páginas, 12 figuras., In 1987, conductivity-temperature-depth and current data were collected in two oceanographic surveys carried out around the Indian Ocean coral atolls of Aldabra (46° 20′ E, 9° 25′ S) and Cosmoledo (47° 30′ E, 9° 45′ S) between April and July. During the surveys, significant changes were observed in the temperature and salinity of the upper layers. From temperature-salinity analysis, the dominant water masses in the upper layers (0–400 m) were categorized and their origin determined. During the first cruise, TS characteristics changed only slightly. Low salinity waters (S = 34.5–34.6 and T = 28°–30°C), brought from the east by the South Equatorial Current, were dominant in the surface layers. During the second cruise, the surface waters were saltier and cooler (S = 35.1 and T = 25°–26°C) and more homogeneous in the upper 200 m as a result of a greater admixture of a southern water mass. Seasonal cooling at this time was responsible for a deeper surface mixed layer. Near the end of the cruise, TS conditions changed suddenly due to an invasion of southern subtropical water masses in the layers above 200 m. Current meter records were dominated by the regional 50-day oscillation and higher-frequency variability and did not show the expected increase in strength of the South Equatorial Current to indicate onset of the southwest monsoon. The water mass changes were not correlated with changes in the local currents and were probably caused by advection of patches by the large-scale flow., The cruises were funded by NERC grant GR3/5549. The first author acknowledges the studentship and support given by the British Council and Instituto de Investigaciones Eléctricas, México.

Oceanic eddy formation behind the tropical island of Aldabra is examined with a one-layer reduced gravity model. Thresholds for flow separation, eddy formation, eddy shedding, and wake instabilities are determined and compared with theory, observations and results of laboratory experiments for both rotating and non-rotating flows. It is shown that non-rotating fluid theory and the Reynolds number are appropriate for describing the occurrence of eddy shedding. For islands at higher latitudes, thresholds move nearer those found in rotating laboratory experiments. Strouhal numbers calculated from the model results agree with those predicted theoretically, confirming that the frequency of eddy shedding does not increase indefinitely with Reynolds number. Both the model results and data from the CZCS archive suggest that eddy shedding and the associated enhanced biological activity (and thus CO 2 uptake) are common phenomena for Aldabra and, by implication, other oceanic islands.

Oceanography in Drake Passage: Wherefrom, Whereto and What in Between?; Liverpool, United Kingdom, 26–27 October 2009; The Antarctic Circumpolar Current (ACC), the world’s largest oceanic flow (~135 million cubic meters per second), is an important component of the ocean climate, as it connects the three major oceanic basins. Deep Atlantic water upwells between the ACC and Antarctica and returns to the Atlantic, thus contributing to the closure of the global overturning circulation. The Drake Passage, between the southern tip of South America and Antarctica, is the region where the ACC is most constricted by landmasses and, owing to its narrowness, is the most convenient place to monitor the ACC. The Drake Passage also has considerable oceanographic interest because it lies along the cold, returning route of the global overturning circulation and is a region of strong deepwater mixing.

The surface eddy kinetic energy field of the North Atlantic subpolar gyre (40–65°N, 5–60°W) is studied using the altimetric satellites Geosat (1987–1988) and ERS-1 (1992–1993). This is, on the whole, an area of low eddy activity; previous studies of the North Atlantic have usually concentrated on the highly variable Gulf Stream system. We review what is known of the surface circulation of the region. We confirm that there is a close relationship between the eddy kinetic energy and the mean currents and that it is strongly constrained by the topography; the eddy field occurs in deep water and follows the contours, particularly around the Flemish Cap. High eddy kinetic energy is seen on the flanks of topography and is higher where the slope is steeper. This is particularly clear on both east and west flanks of the Rockall Plateau. Interannual changes in the currents are revealed by the differences between the Geosat and ERS-1 eddy kinetic energy maps. In some years (1988 and 1992–1993) the northern core of the North Atlantic Current (NAC), usually assumed to be tied to the Charlie Gibbs Fracture Zone (52°N), is considerably weaker and may not exist at all, while in 1987 there is a distinct core here. In 1988 and 1992–1993 the main eddy region shifts farther to the south, to about 49°N in 1988 and 50°N in 1992–1993. In 1987 there is also a current core even farther south, centered at about 47°N, implying that in that year the NAC is arranged into two distinct branches.

Paper number 1999JC900333 Coherence analysis techniques are used to compare Southern Ocean wind forcing with Antarctic Circumpolar Current transport. Winds are derived from five different products: ERS winds that have been bin-averaged, weekly gridded ERS winds produced by the Centre ERS d'Archivage et de Traitement, 5 day winds from the Special Sensor Microwave Imager, analysis winds from the European Centre for Medium-Range Weather Forecasts, and reanalysis winds from the National Centers for Environmental Prediction. Barotropic transport is estimated from the pressure difference between bottom pressure gauges deployed on either side of Drake Passage by Proudman Oceanographic Laboratory as part of the World Ocean Circulation Experiment. Surface transport is estimated from TOPEX altimetry. Results indicate that transport and wind forcing are coherent over a broad range of frequencies, corresponding to time periods of roughly 10-256 days. Highest coherences occur for winds at latitudes on the south side of Drake Passage. Barotropic ocean transport lags wind forcing not by a constant time interval but by a constant phase lag of about one eighteenth of a cycle at a broad range of frequencies, suggesting that the oceanic response to wind is controlled by both the tendency term and a frequency dependent viscous process. Surface transport lags by a longer phase interval. Wind stress curl north of Drake Passage is more coherent with transport than is wind stress curl in the latitudes of Drake Passage. Ocean transport lags wind stress curl, suggesting that transport fluctuations are not governed by a simple Sverdrupian vorticity balance. Like the observations, general circulation model transports from the Parallel Ocean Program and from the Parallel Ocean Climate Model are coherent with wind stress from the south side of Drake Passage and with wind stress curl from latitudes north of Drake Passage. Unlike the observations, model transport and bottom pressure vary almost simultaneously with the wind and do not replicate the observed phase lags, implying that the effective model viscosity may be too large.

Chlorophyll absorbs solar radiation in the upper ocean, increasing the mixed layer radiative heating and sea surface temperatures (SST). Although the influence of chlorophyll distributions in the Arabian Sea on the southwest monsoon has been demonstrated, there is a current knowledge gap regarding how chlorophyll distributions in the Bay of Bengal influence the southwest monsoon. The solar absorption caused by chlorophyll can be parameterized as an optical parameter, h2, which expresses the scale depth of the absorption of blue light. Seasonally and spatially varying h2 fields in the Bay of Bengal were imposed in a 30-year simulation using an atmospheric general circulation model coupled to a mixed layer thermodynamic ocean model in order to investigate the effect of chlorophyll distributions on regional SST, the southwest monsoon circulation, and precipitation. There are both direct local upper-ocean effects, through changes in solar radiation absorption, and indirect remote atmospheric responses. The depth of the mixed layer relative to the perturbed solar penetration depths modulates the response of the SST to chlorophyll. The largest SST response of 0.5 ∘C to chlorophyll forcing occurs in coastal regions, where chlorophyll concentrations are high (> 1 mg m−3), and when climatological mixed layer depths shoal during the inter-monsoon periods. Precipitation increases significantly (by up to 3 mm d−1) across coastal Myanmar during the southwest monsoon onset and over northeast India and Bangladesh during the Autumn inter-monsoon period, decreasing model biases.

A survey of the current field over the South Scotia Ridge, obtained with a lowered Acoustic Doppler Current Profiler (LADCP), is presented. There is a pattern of northward (southward) flow on the western (eastern) side of each of four deep passages in the ridge, which is supported by tracer measurements. The net full-depth LADCP-referenced geostrophic transport over the ridge is 22±7 Sv (1 Sv=10 6 m 3 s −1 ) northward, with the jets on either side of the passages transporting 5–10 Sv in alternating directions. The corresponding Weddell Sea Deep Water (WSDW) transport over the ridge is 6.7±1.7 Sv. This is a factor of 4 larger than the only previous estimate in the literature, and suggests that a significant proportion of the Antarctic Bottom Water (AABW) invading the world ocean abyss escapes the Weddell Sea via the Scotia Sea. The net full-depth and WSDW transports over the ridge are modified to 7±6 and 4.7±0.7 Sv, respectively, by a box inverse model of the western Weddell Gyre. The model incorporates the WOCE A23 crossing of the central part of the gyre and a set of five constraints synthesizing our previous oceanographic knowledge of the region. It diagnoses that 9.7±3.7 Sv of AABW are formed in the Weddell Sea, and that comparable amounts are exported over the South Scotia Ridge (∼48%) and further east (∼52%) assuming that no AABW enters the Weddell Gyre from the Indian Ocean. The WSDW fraction with neutral density γ n >28.31 kg m −3 transported over the ridge upwells in the Scotia Sea at a rate of 6×10 −6 m s −1 , an order of magnitude larger than many basin-scale estimates of deep upwelling in the literature. In contrast, the Weddell Sea Bottom Water exported to the eastern Weddell Gyre entrains upward at a rate of 8×10 −7 m s −1 , more typical of other open-ocean regions. When their different ventilation histories are considered, the comparable transports and disparate upwelling rates of the AABW exported over the South Scotia Ridge and farther east may be crucial to our understanding of teleconnections between the Weddell Sea and the global ocean.