Eastern Subtropical North Atlantic Research Articles

Downward particle fluxes within different productivity regimes off the Mauritanian upwelling zone (EUMELI program)

A 2-yr record of downward particle flux was obtained with moored sediment traps at several depths of the water column in two regions characterized by different primary production levels (mesotrophic and oligotrophic) of the eastern subtropical North Atlantic Ocean. Particle fluxes, of ∼71–78% biogenic origin (i.e. consisting of CaCO 3, organic matter and opal) on average, decrease about six-fold from the mesotrophic site (highest fluxes in the North Atlantic) nearer the Mauritanian margin (18°30′N, 21°00′W) to the remote, open-ocean, oligotrophic site (21°00′N, 31°00′W). This decrease largely reflects the difference in total primary production between the two sites, from ∼260 to ∼110 g organic C m −2 yr −1. At both sites, temporal variability of the downward particle flux seems to be linked to westward surface currents, which are likely to transport seaward biomass-rich water masses from regions nearer the coast. The influence of coastal upwelling is marked at the mesotrophic site. The large differences between the 1991 and 1992 records at that site, where carbon export is large, underscore the interest of long-term studies for export budget estimates. The different productivity regimes at the two sites seem to induce contrasting downward modes of transport of the particulate matter, as shown in particular by the faster settling rates and the higher E ratio (particulate organic carbon export versus total primary production) estimated at the mesotrophic site.

Synchronous palynological changes in early pleistocene sediments off new jersey and Iberia, and a possible paleoceanographic explanation

Palynomorphs record the establishment of modern conditions in the subtropical North Atlantic during the early Pleistocene. Prior to ‐1.4 Ma, muds on both the New Jersey shelf and the Iberia Abyssal Plain contained relatively few terrestrial palynomorphs, and had a dinocyst flora rich in Operculodinium israelianum and other dinocyst taxa recording warmer surface waters than at present (e.g., Tectatodinium pellitum, Lingulodinium machaerophorum, and Polysphaeridium zoharyi). Over a span of ‐250 ka, this palynological assemblage was succeeded by one rich in pollen and with a dinocyst flora similar to the “modern”; flora, i.e. rich in Operculodinium centrocarpum, Bitectatodinium tepikiense, Spiniferites spp. (predominantly S. ramosus), and Brigantedinium spp. (predominantly B. simplex). The synchronous palynological changes in such different geological settings in the eastern and western subtropical North Atlantic are attributed to global climatic deterioration and the expansion of ice sheets in the northern hemisphere. Climatic cooling increased the velocity of the Gulf Stream and other surface currents in the subtropical gyre, causing the gyre to contract and pull away from the continents. Glacioeustatically lowered sea levels also exposed a large percentage of the continental shelf areas, and together with other bathymetric highs like the Charleston Bump, deflected the gyre boundary currents (like the Gulf Stream) offshore. Consequently, surface waters of polar origin were able to penetrate between the warm waters of the gyre and the North American continent north of Cape Hatteras in the west, and Iberia in the east, around 1.4 Ma. This paleoceanographic change increased the area of “neritic”; sedimentation at mid latitudes in the North Atlantic, allowing greater terrestrial influx beyond the shelfbreak.

Formation of an Azores Current Due to Mediterranean Overflow in a Modeling Study of the North Atlantic

A mechanism for the formation of the Azores Current is proposed. On the basis of observations and model results, it is argued that the primary cause of the Azores Current is the water mass transformation associated with the Mediterranean overflow in the Gulf of Cadiz. Observations show that the transport of the Mediterranean outflow water through the Strait of Gibraltar increases significantly as it descends the continental slope by entraining the overlying North Atlantic Central Water. This entrainment process introduces a sink at the eastern boundary to the ocean upper layer in addition to the inflow into the Mediterranean. Such a sink is capable of inducing strong zonal flows such as the Azores Current. This mechanism is confirmed by numerical experiments with and without the representation of the Mediterranean overflow process. The numerical model is based on the Miami Isopycnic Coordinate Ocean Model. The model does not include the Mediterranean overflow explicitly, but restores the model density fields in the Gulf of Cadiz toward the observations. This restoring condition produces a reasonable representation of the water mass transformation deduced from observations. The formation of the Azores Current in response to the water mass transformation in the Gulf of Cadiz suggests that the Mediterranean overflow is not only a source of warm and saline water at depth, but also has a strong dynamic impact on the ocean upper layer. This study emphasizes the need to improve the representation of the Mediterranean overflow process in general circulation models in order to capture the correct characteristics of the flow fields and water masses in the subtropical eastern North Atlantic.

Transport of airborne lithogenic material down through the water column in two contrasting regions of the eastern subtropical North Atlantic Ocean

Downward particle fluxes were measured using deep‐moored sediment traps deployed in two regions of contrasting primary productivity levels (mesotrophic and oligotrophic) of the eastern subtropical North Atlantic Ocean. The high percentage of lithogenic material (∼20–30% on average) in the paniculate matter collected shows the regional significance of the atmospheric dust inputs originating from West Africa. The magnitudes of lithogenic and biogenic fluxes decrease ∼5–6 and ∼8–9 fold, respectively, from near the African margin (mesotrophic region) to the remote open ocean (oligotrophic region). These trophic differences seem to give rise to differences in the characteristics of the downward transport of lithogenic material. At the oligotrophic site, the relatively low and slow export of biogenic matter apparently limits and delays the removal of lithogenic particles delivered to surface waters from the atmosphere. In contrast, the higher biological activity in the mesotrophic region seems to provide persistent conditions for an efficient and faster downward transport of the deposited lithogenic particles, and the temporal variability of lithogenic fluxes largely reflects that of the atmospheric dust inputs. Thus whether the temporal variability of the exported lithogenic flux in the water column follows that of the atmospheric deposition appears to depend on the trophic status. In the mesotrophic region the oft‐observed linear relationship between lithogenic and particulate organic matter (hereinafter POM) fluxes breaks down at high POM fluxes. This observation adds weight to the idea that linear relationships between POM fluxes and some candidate proxies for POM transfer cannot be assumed when POM export is large. A high mesoscale variability of biogenic, but not lithogenic, fluxes in the water column of the mesotrophic region underscores the relevance of mesoscale studies for regional estimates of export of biogenic material.

SYNCHRONOUS PALYNOLOGICAL CHANGES IN EARLY PLEISTOCENE SEDIMENTS OFF NEW JERSEY AND IBERIA, AND A POSSIBLE PALEOCEANOGRAPHIC EXPLANATION

Palynomorphs record the establishment of modern conditions in the subtropical North Atlantic during the early Pleistocene. Prior to ~1.4 Ma, muds on both the New Jersey shelf and the Iberia Abyssal Plain contained relatively few terrestrial palynomorphs, and had a dinocyst flora rich in Operculodinium israelianum and other dinocyst taxa recording warmer surface waters than at present (e.g., Tectatodinium pellitum, Lingulodinium machaerophorum, and Polysphaeridium zoharyi). Over a span of ~250 ka, this palynological assemblage was succeeded by one rich in pollen and with a dinocyst flora similar to the “modern” flora, i.e. rich in Operculodinium centrocarpum, Bitectatodinium tepikiense, Spiniferites spp. (predominantly S. ramosus), and Brigantedinium spp. (predominantly B. simplex). The synchronous palynological changes in such different geological settings in the eastern and western subtropical North Atlantic are attributed to global climatic deterioration and the expansion of ice sheets in the northern hemisphere. Climatic cooling increased the velocity of the Gulf Stream and other surface currents in the subtropical gyre, causing the gyre to contract and pull away from the continents. Glacioeustatically lowered sea levels also exposed a large percentage of the continental shelf areas, and together with other bathymetric highs like the Charleston Bump, deflected the gyre boundary currents (like the Gulf Stream) offshore. Consequently, surface waters of polar origin were able to penetrate between the warm waters of the gyre and the North American continent north of Cape Hatteras in the west, and Iberia in the east, around 1.4 Ma. This paleoceanographic change increased the area of “neritic” sedimentation at mid latitudes in the North Atlantic, allowing greater terrestrial influx beyond the shelfbreak.

Influence of the North Atlantic SST on the atmospheric circulation

Using the monthly COADS dataset and NMC‐NCAR archives we show that significant anomalies of the atmospheric circulation are related to previous SST anomalies in the North Atlantic. A signal over the northwest Labrador Sea in late spring is associated with the dominant mode of SST variability during the preceeding winter. It is more clearly seen in the mid‐troposhere than at sea level and appears to be related to the anomalous surface heat exchanges that slowly damp the SST anomalies. In addition, a NAO‐like signal in early winter is associated with SST anomalies east of Newfoundland and in the eastern subtropical North Atlantic during the preceeding summer.

Depth-integrated primary production in the eastern tropical and subtropical North Atlantic basin from ocean colour imagery

Existing satellite numerical models and data interpolation methods were used to evaluate the scales of variation in the vertical distribution of the phytoplankton biomass and the daily rate of primary production within the subtropical and tropical NE Atlantic Ocean (5-40 N; 6-30 W). The choice of this area was dictated principally by its economical importance, as it represents a large fishing ground due to upwelling activities along the coast of Morocco and Mauritania. After geographical partition of the area of study into 'bio-geochemical provinces' based on bathymetry and surface circulation, up to 300 satellite scenes obtained from the defunct Coastal Zone Color Scanner (CZCS) and covering the full year 1983 were processed into maps of surface chlorophyll and were further analysed into integrated primary production. Analyses of satellite data included a specific method to account for the sensitivity loss of the sensor during the studied period. The results of the productivity model are presented in terms of seasonal variations in the daily and annual photosynthetic carbon production in the various provinces and their contribution to the productivity of the overall study area. A total of 0.82 GtC y-1 was computed for the subtropical and tropical NE Atlantic. One third of this is produced within the coastal zone although it accounts for only 14% of the total area.

Studying subtropical thermocline ventilation and circulation using tritium and 3He

A 13‐year time series of tritium and 3He in the Sargasso Sea near Bermuda shows the downward penetration of the bomb tritium and excess 3He maxima into the main thermocline at a rate of about 17 m yr−1. A simple box‐mixing model effectively mimics both the evolution of the tracer maxima and their thermocline inventories. The thermocline inventory of ζ (the sum of tritium and 3He) near Bermuda has halved over duration of the time series. This can be used to estimate a regional average nitrate efflux from the main thermocline of 0.7±0.2 mol (N) m−2 yr−1. In the eastern subtropical North Atlantic I combine 3H‐3He age with salinity, oxygen, and geostrophy to compute isopycnal diffusivities, oxygen consumption rates, and absolute velocities. The reference level velocities are determined almost solely by the 3H‐3He age equations and to an accuracy of about 1 mms−1. A classic absolute velocity spiral is seen. The depth variation of computed vertical velocities is consistent with vorticity conservation and extrapolates to within errors of surface Ekman pumping and local subduction rates. Isopycnal diffusivities are largely constrained by the salinity equations and are ∼1200 m2 s−l at a depth of 300 m, decreasing gradually downward. Diffusivities apparently decrease toward the surface, likely an artifact of unsteadiness in the salinity equations. The oxygen utilization rates (OURs) determined by the oxygen equations decrease exponentially with depth. Vertical integration of OUR yields a net water column oxygen demand of 4.1±0.8 mol m−2 yr−1, which corresponds to an export production of 2.5±0.5 mol m−2 yr−1 carbon. I present a simple scheme to show how to relate the vertical profiles of 3H‐3He age to the subduction rate as a function of depth projected back to the surface outcrop. The shallowest horizon has a subduction rate indistinguishable from local climatological Ekman pumping rates but gradually exceeds the projected rates with depth. The difference may be attributed to the increasing importance of buoyancy‐forced subduction at higher latitudes.

129I in archived seawater samples

Anthropogenic 129I (t1/2=15.7My) discharged by the nuclear fuel reprocessing facilities at Sellafield (UK) and La Hague (France) is a promising tracer of physical and biogeochemical processes in the North Atlantic and Arctic Oceans. To improve understanding of its releases and dispersal, 129I was measured in archived seawater samples that had been collected as part of previous tracer studies, thus allowing direct comparison of 129I with other anthropogenic radionuclides. A sample collected in the eastern subtropical North Atlantic in 1969 was selected in order to directly measure the impact of weapons-fallout 129I in the oceans. The measured 129I/127I ratio of the sample is 0.53±0.08×10-10 (0.53±0.08IU: 1IU≡129I/127I=10-10), compared to the pre-anthropogenic ratio of ∼10-12 (0.01 IU). The ratio of 129I to 137Cs is 2.0±0.6 (atom ratio), 1.6±0.6 when corrected for 7yr of radioactive decay from the bomb-input peak. This observed ratio is ten times higher than predicted from fission yields, possibly reflecting the greater volatility of iodine relative to cesium. 129I/137Cs ratios in Scottish and Norwegian Coastal waters, sampled in 1976 and 1978, are in good agreement with predictions based on the available release data. Reprocessing 129I is clearly seen in the northern Greenland Sea (>6 IU) and in Denmark Straits Overflow Water (1.4 IU) in samples collected during the TTO/NAS program in 1981. The strength of the tracer signal in the overflow water – the ratio of the concentration in the overflow core to its minimum value in the station profile – is approximately four times higher for 129I than for the other tracers measured (137Cs, 90Sr, and 3H).

Observations of Surface Forcing from the Subduction Experiment: A Comparison with Global Model Products and Climatological Datasets*

Abstract Reliable estimates of the exchange of heat, moisture, and momentum across the air–sea interface are essential in assessing the local “representativeness” of the surface forcing fields depicted by global model and climatological datasets. The reliability and extended length of the in situ data collected by a large-scale array of buoys deployed during the Subduction Experiment make this dataset particularly well suited to providing such an assessment. The Subduction Experiment was designed to explore the process by which the mixed layer waters of the eastern subtropical North Atlantic are incorporated into the top of the main thermocline. To this end, an array of five buoys was maintained between 18°–33°N and 22°–34°W from June 1991 to June 1993. In situ dynamic, thermodynamic, and radiometric measurements are utilized along with a state-of-the-art bulk flux algorithm to estimate the time-dependent surface forcing at each of the buoys. The resulting air–sea fluxes are compared to similar quantities...

Deep water particle flux in the Canary Island region: seasonal trends in relation to long-term satellite derived pigment data and lateral sources

We present a 3 year record of deep water particle flux at the recently initiated ESTOC (European Station for Time-series in the Ocean, Canary Islands) located in the eastern subtropical North Atlantic gyre. Particle flux was highly seasonal, with flux maxima occurring in late winter-early spring. A comparison with historic CZCS (Coastal Zone Colour Scanner) data shows that these flux maxima occurred about 1 month after maximum chlorophyll was observed in surface waters in a presumed primary source region 100 km × 100 km northeast of the trap location. The main components of the particles collected with the traps were mineral particles and carbonate, both correlating strongly with organic matter sedimentation. Mineral particles in the sinking matter are indicative of the high aeolian input from the African desert regions. Comparing particle fluxes at 1 km and 3 km depth, we find that particle sedimentation increased substantially with depth. Yearly organic carbon sedimentation was 0.6 g m−2 at 1 km depth compared with 0.8 g m−2 at 3 km. We hypothesize that higher phytoplankton biomass observed further north could be a source of laterally advecting particles that interact with fast sinking particles originating from the primary source region. This hypothesis is also supported by the differences in size distribution of lithogenic matter found at the two trap depths.

The Eastern Subtropical Gyre (North Atlantic): Flow Rings Recirculations Structure and Subduction

Thirteen carefully prepared drogued buoy assemblies have been deployed in the eastern subtropical North Atlantic giving ~20 buoy years of Lagrangian data at a depth of 200 m. The buoy results together with hydrography have revealed the structure of the eastward flowing Azores Current (AC). The main jet had a transport of 26 Sv (near 28°W) with compensating counterflows in March 1992. Jet and counterflows were readily seen in the ADCP current structure and evident in the upper layer temperature (salinity) structure on an isopycnal surface. Buoys and hydrography showed that the adjacent westward flowing counterflows resulted in recirculation both north (anticlockwise circulation) and south (clockwise circulation) of the AC - the Subtropical Recirculations. South-south-west flow (3 cm s−1) occurred in the central region of study west of the Canary Islands. The long-term movement measured in the south or northern North Equatorial Current region was 3·5 cm s−1west-south-west. The mean south displacement per year of the buoys was 2·2° of latitude to the south and most of this displacement occurred in the first half of the year (February-August). The maximum westward displacement rate occurred six months later in October and November. The Subtropical Front/Azores Current region was identified as a zone of increased levels of kinetic energy (>100 cm2s−2) at a latitude near 34°N at the 200 m level, stretching for >2000 km, and as a marked horizontal winter sea surface temperature contrast at a latitude near 36°N. Winter mixing created an outcropping region of water with density in the range 26–4<σ0<26·6 kg m−3along the Subtropical Front near 34°N with a maximum vertical extent of 200 m.

Hydrogen peroxide in the marine atmospheric boundary layer during the Atlantic Stratocumulus Transition Experiment/Marine Aerosol and Gas Exchange experiment in the eastern subtropical North Atlantic

Gas phase H2O2 was measured in surface air on the NOAA ship Malcolm Baldrige from June 8 to 27, 1992 (Julian days 160–179), during the Atlantic Stratocumulus Transition Experiment/Marine Aerosol and Gas Exchange experiment in the eastern subtropical North Atlantic region. Average H2O2 mixing ratios observed were 0.63±0.28 ppbv, ranging between detection limit and 1.5 ppbv. For the entire experiment, only weak or no correlation was found between H2O2 mixing ratio and meteorological parameters (pressure, temperature, humidity, or UV radiation flux) as well as with tracers of continental air masses (CO, black carbon, radon). The average daily H2O2 cycle for the entire period exhibits a maximum of 0.8±0.3 ppbv near sunset and a minimum of 0.4±0.2 ppbv 4–5 hours after sunrise. Several clear H2O2 diurnal variations have been observed, from which a first‐order removal rate of about 1×10−5 s−1 for H2O2 can be inferred from nighttime measurements. This rate compares well with those deduced from measurements taken at Cape Grim (Tasmania, 41°S) and during the Soviet‐American Gas and Aerosol III experiment (equatorial Pacific Ocean).

Will Deep Subtropical Ring ‘Storm Physallv’ Cross the Mid Atlantic Ridgea and Reach America?

A short research cruise was planned to trace the movement of a discrete body of water in the subtropical eastern North Atlantic Ocean. A subtropical ring or deep eddy called STORM was found budding off the Subtropical Front (STF) south-west of the Azores. A physical, chemical and biological survey to depths of 3·5 km was made of this 400 km scale body of water which was spinning cyclonically (anticlockwise). The azimuthal transport or the amount of water swirling in the eddy was 45 Sv. Storm was ‘hooked’ with ten drogued Argos buoys and a further five subsurface Alace floats were deployed. Storm is moving westward at ~3 km a day and is expected to reach the Mid Atlantic Ridge in rather less than a year unless it is destroyed by typography or reabsorbed into the Azores Current. With current technology, Storm's evolution and westward progress can be observed and analysed remotely, at a distance of ~3000 km in the laboratory. Realtime position data means that future sea surveys can be planned.

Observations of Temperature Microstructure in NATRE

Abstract A new autonomous instrument collected 76 profiles of temperature microstructure over a ten-day period in the eastern subtropical North Atlantic as part of the North Atlantic Tracer Release Experiment. The data between 200-m and 350-m depth was used to determine the mean rate of temperature variance dissipation 〈χ〉. The estimated diapycnal diffusivity is Ky = 1.4×10−5 m2 s−1. The distribution of χ is approximately lognormal, suggesting that the 95% confidence limits on 〈χ〉 are ±4%. This uncertainty is less than that caused by the imperfectly known probe response, possible noise spikes on the probes, and variability in the degree of microstructure anisotropy; the latter two effects were estimated from a pair of closely spaced probes. Each of these uncertainties is about ±15%. Statistically significant low-frequency variability of χ is observed with 〈χ〉 decreasing by a factor of 2 between the first and second half of the observation. This low-frequency variability is likely the largest cause of erro...

Nitrate use by plankton in the eastern subtropical North Atlantic, March‐April 1989

Nitrate concentration was measured in seawater samples from the euphotic zone at the beginning and end of 12‐h, daytime, in situ incubations. The changes in concentration are considered to be measurements of new production. During periods of 2–3 weeks in March–April 1989, important time scales for NO3− input to the euphotic zone (i.e. residence times) and new production were ~26 d at 18°N, 31°W and ~10 d near 33°N, 21°W. The average rate of NO3− use in the two areas was 2.63 and 0.62 mmol N m−2 (12 h)−1, or, in carbon equivalents 209 and 49 mg C m−2 d−1, respectively. These values bracket the large‐scale estimate by Jenkins of new production in the nearby beta triangle of 150 mg C m−2 d−1.

Seasonal variability of meridional temperature fluxes in the eastern North Atlantic Ocean

Seasonal meridional ocean temperature fluxes were computed in a regional study of the eastern North Atlantic Ocean east of 30°30′W between 12°30′N and 39°30′N for the upper 1500 m of the ocean. Historical oceanographic and meteorological measurements are the data base for the direct method of computing temperature fluxes. Seasonal changes in temperature fluxes caused by the seasonality of Ekman transport and geostrophic transport are strongly dependent on latitude. Between 19N and 25N the meridional temperature flux shows low seasonality. In this area the permanent subtropical gyre and the stable trade-winds result in low seasonal changes. North of 25N the Ekman transport shows large seasonal variations. The latitude of the transition of southward Ekman temperature flux to northward Ekman temperature flux is located at 28N in winter. In summer it is found at 38N. The seasonal variability of the meridional temperature fluxes in the subtropics north of 25N is influenced by this annual cycle in Ekman transport, as well as by the southward displacement in summer and the northward movement of the Azores Current in winter. The tropical eastern Atlantic Ocean shows seasonal changes both in the geostrophic and Ekman transports. South of 17N the total temperature flux is always to the north. The largest meridional temperature fluxes, with more than 0.7 PW, are found in fall at 12°30′N directed northward, and in winter at 33°30′N to the south. In general the subtropical eastern North Atlantic Ocean transports heat to the south all the year round, while in the tropics heat is transported to the north. The seasonality in the eastern Atlantic Ocean is found to be different from seasonal variations in global investigations. The seasonal heat budget computations show a heat gain in the ocean in the area investigated from April to September and a heat loss from October to March. Over the whole year the eastern North Atlantic gains about 0.09 PW from the atmosphere.

3H and3He in the Beta Triangle: Observations of Gyre Ventilation and Oxygen Utilization Rates

Isopycnal maps of 3H–3He age (τ) with about 100 km resolution have been obtained for a 1000-km scale area in the eastern subtropical North Atlantic. The midscale texture of the maps is consistent with isopycnal diffusivities of order 500 m−2 s−1. Analysis of the distributions within the context of advection-diffusion equations reveals that the larger scale 3H–3He age gradients observed within the area are not seriously affected by mixing on those surfaces that outcrop in the region of Ekman downwelling. Thus, isopycnal velocities can be estimated from 1/∇τ, but record only the velocity component normal to the outcrop. The velocities thus obtained agree well with geostrophic estimates, although the comparison is flawed by the fundamental mismatch in timescales between the two techniques. Backward extrapolation of the maps to zero-age outcrop positions indicate that the contribution of unventilated, older, recirculated water to the gyre flow above 600 m depth is small in this area (no more than 20%). Ventilation of these density horizons thus is two to three times greater than inferred from Ekman pumping alone. A simple argument concerning the interaction of large scale flow with the topography of the depth of winter mixing shows that it is consistent with this process being a primary ventilation/subduction process for the subtropical gyre thermocline. Advection–diffusion analysis of the AOU distributions on these surfaces indicates that oxygen utilization rates may be estimated using δAOU/δτ to an accuracy of order 10%. Such estimates appear consistent with previous work, and curvature in the AOU versus τ relationship may be a reflection of a southeastward increase in surface primary productivity.

Meridional temperature fluxes in the subtropical eastern North Atlantic

In a regional study of the eastern North Atlantic Ocean east of 35°W between 41°N and 8°N the mean meridional ocean temperature flux was computed from oceanographic and meteorological measurements using the direct method. In the area of the permanent subtropical gyre between 36°N and 22°N, a southward geostrophic temperature flux dominates. The Ekman temperature flux is weak and changes from a southward flux north of 32°N to a northward flux south of 32°N. In the area of the North Equatorial Current and in the tropics the Ekman temperature flux is comparable in magnitude to the geostrophic temperature flux. Therefore, the total temperature flux changes to a northward direction at 20°N, where the geostrophic transport is still to the south, and becomes large in the tropics, where both components show northward temperature fluxes. The heat flux divergence for the area investigated leads to an ocean heat gain of 0.19 PW. A comparison of annual mean temperature fluxes with temperature fluxes of east-west CTD sections from the winter half-year shows a small seasonal signal in the geostrophic temperature flux in the subtropical gyre but large differences in the tropics. The seasonal changes for the Ekman temperature fluxes are weak.

Climatic effects of late‐glacial surges based on the example of the 10,500 b p: Cold phase

Abstract A map of paleotemperature anomalies at 10,500 B.P. for the North Atlantic and adjacent continents was compiled. It is based upon data from marine micropaleontological and palynological studies. The pattern of isotherms reveals that maximum negative anomalies occurred in the eastern subtropical North Atlantic between 35 and 45°N, reaching values of 8–9°C, i.e., double those recorded over the adjacent landmasses (2–4°C). The area of maximum lowering of sea surface temperatures was located only some 5° south of the zone of highest accumulation rates of iceberg‐rafted sands. On land the area of maximum cooling coincided with the zone affected by Mediterranean cyclones. In the eastern part of the ocean, off the European and African coasts the sea surface isotherms diverged northwards and southwards, suggesting that there was a bifurcation in a westerly cold current at the latitude of about Lisbon. All these features are inconsistent with “traditional”; concepts of paleotemperature anomalies associated...