Warm Water Layer Research Articles

Study of the heat flux at the water-bottom sediments in Amurskiy Bay in the Sea of Japan in the winter season

The results of the temperature profiles and heat flux field studies in the upper layer of the bottom sediments of Amurskiy Bay in the Sea of Japan are presented. These studies were carried out from November 22 to March 25, 2010. The obtained values of the heat flux from the sediments to the water layer can explain the formation of the warm water layer with high salinity near the bottom in Amurskiy Bay during the winter season.

Heat loss from the Atlantic water layer in the northern Kara Sea: causes and consequences

Abstract. A distinct, subsurface density front along the eastern St. Anna Trough in the northern Kara Sea is inferred from hydrographic observations in 1996 and 2008–2010. Direct velocity measurements show a persistent northward subsurface current (~ 18 cm s−1) along the St. Anna Trough eastern flank. This sheared flow, carrying the outflow from the Barents and Kara seas to the Arctic Ocean, is also evident from shipboard observations as well as from geostrophic velocities and numerical model simulations. Although we cannot substantiate our conclusions by direct observation-based estimates of mixing rates in the area, we hypothesize that the enhanced vertical mixing along the St. Anna Trough eastern flank favors the upward heat loss from the intermediate warm Atlantic water layer. Modeling results support this hypothesis. The upward heat flux inferred from hydrographic data and model simulations is of O(30–100) W m−2. The region of lowered sea ice thickness and concentration seen both in sea ice remote sensing observations and model simulations marks the Atlantic water pathway in the St. Anna Trough and adjacent Nansen Basin continental margin. In fact, the sea ice shows a delayed freeze-up onset during fall and a reduction in the sea ice thickness during winter. This is consistent with our results on the enhanced Atlantic water heat loss along the Atlantic water pathway in the St. Anna Trough.

Dansgaard‐Oeschger cycles: Interactions between ocean and sea ice intrinsic to the Nordic seas

Dansgaard‐Oeschger (D‐O) cycles are the most dramatic, frequent, and wide‐reaching abrupt climate changes in the geologic record. On Greenland, D‐O cycles are characterized by an abrupt warming of 10 ± 5°C from a cold stadial to a warm interstadial phase, followed by gradual cooling before a rapid return to stadial conditions. The mechanisms responsible for these millennial cycles are not fully understood but are widely thought to involve abrupt changes in Atlantic Meridional Overturning Circulation due to freshwater perturbations. Here we present a new, high‐resolution multiproxy marine sediment core monitoring changes in the warm Atlantic inflow to the Nordic seas as well as in local sea ice cover and influx of ice‐rafted debris. In contrast to previous studies, the freshwater input is found to be coincident with warm interstadials on Greenland and has a Fennoscandian rather than Laurentide source. Furthermore, the data suggest a different thermohaline structure for the Nordic seas during cold stadials in which relatively warm Atlantic water circulates beneath a fresh surface layer and the presence of sea ice is inferred from benthic oxygen isotopes. This implies a delicate balance between the warm subsurface Atlantic water and fresh surface layer, with the possibility of abrupt changes in sea ice cover, and suggests a novel mechanism for the abrupt D‐O events observed in Greenland ice cores.

Seismic imaging of the upper ocean

In recent years, seismic imaging has become a commonly used method to observe fine‐scale ocean structures. In this technique, sound waves are generated and reflected off oceanographic structures such as the thermocline, the layer separating warm surface waters from colder, deeper waters. The reflectivity of the thermocline is determined by its thickness and the temperature difference between the warm surface water and colder layers below; by examining the properties of the reflected sound waves, scientists can get a picture of the thermocline structure.

Impact of Atmospheric Forcing on Antarctic Continental Shelf Water Masses

Abstract The Antarctic continental shelf seas feature a bimodal distribution of water mass temperature, with the Amundsen and Bellingshausen Seas flooded by Circumpolar Deep Water that is several degrees Celsius warmer than the cold shelf waters prevalent in the Weddell and Ross Seas. This bimodal distribution could be caused by differences in atmospheric forcing, ocean dynamics, ocean and ice feedbacks, or some combination of these factors. In this study, a highly simplified coupled sea ice–mixed layer model is developed to investigate the physical processes controlling this situation. Under regional atmospheric forcings and parameter choices the 10-yr simulations demonstrate a complete destratification of the Weddell Sea water column in winter, forming cold, relatively saline shelf waters, while the Amundsen Sea winter mixed layer remains shallower, allowing a layer of deep warm water to persist. Applying the Weddell atmospheric forcing to the Amundsen Sea model destratifies the water column after two years, and applying the Amundsen forcing to the Weddell Sea model results in a shallower steady-state winter mixed layer that no longer destratifies the water column. This suggests that the regional difference in atmospheric forcings alone is sufficient to account for the bimodal distribution in Antarctic shelf-sea temperatures. The model prediction of mixed layer depth is most sensitive to the air temperature forcing, but a switch in all forcings is required to prevent destratification of the Weddell Sea water column.

춘계 베링해 알류산 해분의 해양환경 특성

The characteristics of the oceanographic environment in the Aleutian Basin of the Bering Sea during spring in 1996, 1997, and 1999 were clarified. An investigation of the water properties revealed five basic layers in the Bering Sea during spring: (1) a surface layer of warm and low-salinity water induced by solar heating, (2) a subsurface layer of cold and low-salinity water propagated slowly by heat from the surface layer, (3) a thermocline layer where salinity was constant but temperature sharply decreased, (4) a temperature inversion layer, and (5) a deep layer with a gradual decrease in temperature and increase in salinity toward the bottom. The ranges of water temperature and salinity were and 31.81-34.08 in 1996, and 31.9-34.06 in 1997, and and 32.0-34.11 in 1999, respectively. The water temperature of the surface layer was approximately higher in 1997 than in 1996 and 1999. The lowest temperature at a depth of 100-150 m was about lower in 1999 than in 1996 and 1997. Nutrient levels (nitrate, phosphate, and silicate) contributing to the control of the growth of phytoplankton were higher in the Aleutian Basin than in the eastern continental shelf and Bogoslof Island area. This was closely associated with the phytoplankton distribution. Nutrient concentrations were lowest at a depth of 25 m. The high primary production at that depth was confirmed from the vertical distribution of chlorophyll a. Chlorophyll a levels were above in some areas in 1996 and 1999, but below in most areas in 1997. Zooplankton density was about three times higher in 1999 than in 1997.

Simulated Interannual Variations of Freshwater Content and Sea Surface Height in the Beaufort Sea*

Abstract The authors investigate the interannual variations of freshwater content (FWC) and sea surface height (SSH) in the Beaufort Sea, particularly their increases during 2004–09, using a coupled ice–ocean model (CIOM), adapted for the Arctic Ocean to simulate the interannual variations. The CIOM simulation exhibits a (relative) salinity minimum in the Beaufort Sea and a warm Atlantic water layer in the Arctic Ocean, which is similar to the Polar Hydrographic Climatology (PHC), and captures the observed FWC maximum in the central Beaufort Sea, and the observed variation and rapid decline of total ice concentration, over the last 30 years. The model simulations of SSH and FWC suggest a significant increase in the central Beaufort Sea during 2004–09. The simulated SSH increase is about 8 cm, while the FWC increase is about 2.5 m, with most of these increases occurring in the center of the Beaufort gyre. The authors show that these increases are due to an increased surface wind stress curl during 2004–09, which increased the FWC in the Beaufort Sea by about 0.63 m yr−1 through Ekman pumping. Moreover, the increased surface wind is related to the interannual variation of the Arctic polar vortex at 500 hPa. During 2004–09, the polar vortex had significant weakness, which enhanced the Beaufort Sea high by affecting the frequency of synoptic weather systems in the region. In addition to the impacts of the polar vortex, enhanced melting of sea ice also contributes to the FWC increase by about 0.3 m yr−1 during 2004–09.

Summer bacterio- and zooplankton in coastal waters of Svalbard

The distribution of bacterio- and zooplankton was studied in West Spitsbergen (Svalbard) coastal waters in August 2009. The bacterial abundance and biomass varied from 110 to 3360 × 103 cells/ml and from 0.66 to 44.93 mg C/m3, respectively. These values were the highest in the surface water layers and decreased with depth. The greatest abundance of bacteria (5099 individuals/m3) was found in the freshened and warm water layer in Isfjorden. The highest biomass of zooplankton (182.41 mg C/m3) was registered in the zone of interaction of coastal and transformed Atlantic waters in the archipelago inner shelf. The spatial variations of abundance and biomass of the planktonic communities were related to the thermohaline characteristics of the water masses and, probably, to microalgal blooms.

Distribution and some traits of biology of the elongated sculpin Alcichthys elongatus in the north-western part of the Sea of Japan

It has been found, with reference to the data of trawl survey and literature, that, in the Sea of Japan, the Northern boundary of the area of the elongated sculpin Alcichthys elongatus is the central part of the Tatar Strait. During the year, the elongated sculpin occurs at depths from 7 to 650 m. Its highest concentration forms during the feeding period. At this time Alcichthys elongatus stays up to depths 253 m but prefers the range of 40–100 m. It winters below the 50 m isobath, mainly in the lower part of the shelf and in the upper section of the continental slope. Being an eurythermal species, the elongated sculpin occurs in a wide range of temperature (from −1.6 to 17.7°C). However, most specimens prefer waters with slightly positive temperature. Juveniles prefer the warm water layers. Males are larger than females but the latter dominate in catches. According to the kind of diet A. elongatus, it is a benthoichtyophage consuming predominantly decapods (mostly juveniles of Chionoecetes opilio) and small fish. In summer, the value of daily ration is 3.0% of the body weight. In the north-western part of the Sea of Japan, A. elongatus may be characterized as a common species with a low but stable abundance.

Phanerozoic Large Igneous Provinces (LIPs), HEATT (Haline Euxinic Acidic Thermal Transgression) episodes, and mass extinctions

The Phanerozoic consists of three mutually exclusive climate states: Icehouse, Greenhouse, and Hothouse. The Greenhouse is the default state, representing > 70% of the Phanerozoic. It is characterized by a weak thermal mode (pole-driven deep-water formation), with little or no continental sea ice, and weakly oxic cool-water sinking near the poles. Nitrogen limitation characterizes Greenhouse oceans in which ammonium may be the dominant bioavailable form of nitrogen. The steady-state Greenhouse default must be forced to produce either of the other two states. Continent–continent collision produces the intense chemical weathering that draws down atmospheric CO 2 and results in the Icehouse state that comprises 20–25% of the Phanerozoic. Icehouses have ice caps in contact with the ocean that produce icebergs and foster sea-ice formation. Sea-ice formation fills the ocean with highly oxic phosphorus-limited icewater except for a thin layer of warm surface water in the tropics. Of the 23 most conspicuous mass extinctions of the Phanerozoic (including the late Ediacaran), 4 are associated with ice-volume-related regressions, and 3 are problematic. We suggest that the other 16 mass extinctions occurred when Greenhouse climate was forced to Hothouse climate. Large Igneous Provinces (LIPs) can trigger the HEATT (Haline Euxinic Acidic Thermal Transgression) mechanism, which can force Greenhouse climate to a Hothouse climate state. The rapid, voluminous CO 2 emissions of LIPs cause a series of events that result in very slow but pronounced haline-mode circulation (mid-latitude-driven deep-water formation) that produces warm saline bottom water at very dry, hot subtropical and middle latitudes. This water upwells at the poles, causing warm and moist equable climate. Hothouse development promotes deep-sea anoxia that is generated in concert with CO 2 buildup and warming. The spread of anoxia favors reduced nitrogen over nitrate, and limited iron dust curtails nitrogen fixation. This leads to dominance of primary productivity by primitive green algae and/or cyanobacteria. Progression to euxinia that reaches the photic zone severely curtails primary productivity via poisoning, even as availability of usable nitrogen plummets. The result is eukaryotic mass extinction. We suggest that the 16 Phanerozoic mass extinctions referred to above resulted at least in part from the HEATT process. Evidence for this relationship at 11 of the most severe extinctions is convincing. Data sets for the other 5 are strongly suggestive of HEATT-related mass extinction, but do not yet have enough documentation to reliably characterize them as HEATT episodes.

Impact of food concentration on diel vertical migration behaviour of Daphnia pulex under fish predation risk

Vertical migration of Daphnia represents the best-studied predator-avoidance behaviour known; yet the mechanisms underlying the choice to migrate require further investigation to understand the role of environmental context. To investigate the optimal habitat choice of Daphnia under fish predation pressure, first, we selected the individuals exhibiting strong migration behaviour. The animals collected from the hypolimnion during the daytime were significantly larger, being more conspicuous, and in turn performed stronger diel vertical migration (DVM) when exposed to fish cue. We called them strong migrants. Second, we provided the strong migrant D. pulex with food at high and intermediate (1 and 0.4 mg C l−1, respectively) levels, which were well above the incipient limiting level and of high quality. They traded the benefits of staying in the warm water layer and moved down to the cold water in response to fish cue indicating fish predation. The availability of food allowed the animals to stay in the cold hypolimnion. However, at the low food level (0.1 mg C l−1), which is an additional constraint on fitness, Daphnia moved away from the cold hypolimnion. Poor food condition resulted in strong migrant Daphnia to cease migration and remain in the upper warmer water layer. Although temperature is known to be a more important cost factor of DVM than food, our results clearly show that this is only true as long as food is available. It becomes clear that food availability is controlling the direction of vertical positioning when daphnids experience a dilemma between optimising temperature and food condition while being exposed to fish cue. Then they overlook the predation risk. Thus, the optimal habitat choice of Daphnia appears to be a function of several variables including temperature, food levels and fish predation.

Stability and Mixing of a Vertical Axisymmetric Buoyant Jet in Shallow Water

The stability, mixing and effect of downstream control on axisymmetric turbulent buoyant jets discharging vertically into shallow stagnant water is studied using 3D Reynolds-averaged Navier–Stokes equations (RANS) combined with a buoyancy-extended k –e model. The steady axisymmetric turbulent flow, temperature (or tracer concentration) and turbulence fields are computed using the finite volume method on a high resolution grid. The numerical predictions demonstrate two generic flow patterns for different turbulent heated jet discharges and environmental parameters (i) a stable buoyant discharge with the mixed fluid leaving the vertical jet region in a surface warm water layer; and (ii) an unstable buoyant discharge with flow recirculation and re-entrainment of heated water. A stratified counterflow region always appears in the far-field for both stable and unstable buoyant discharges. Provided that the domain radius L exceeds about 6H, the near field interaction and hence discharge stability is governed chiefly by the jet momentum length scale to depth ratio lM/H, regardless of downstream control. The near field jet stability criterion is determined to be lM/H = 3.5. A radial internal hydraulic jump always exists beyond the surface impingement region, with a 3- to 6-fold increase in dilution across the jump compared with vertical buoyant jet mixing. The predicted stability category, velocity and temperature/concentration fields are well-supported by experiments of all previous investigators.

Warming in Arctic intermediate and deep waters around Chukchi Plateau and its adjacent regions in 1999

Based on the data measured during Arctic scientific expedition of China in 1999, the characteristics of temperature and salinity distributions around the Chukchi Plateau and its ad-jacent regions have been studied. It was found that the intermediate water with temperature higher than 0.5℃ existed in all parts of a 640 km section with a maximum temperature of 0.85℃ indicating a strong signal of the warming in Arctic Intermediate Water in 1999. Two important phenomena are described in this paper. First, the temperature of warm water was horizontally nonuniform. In the area of Chukchi Plateau, the temperature was higher, the layer of warm water was thicker and the depth of the warm water core was shallower than those in the area of con-tinental slope. The horizontal nonuniformity of the temperature distribution of warming water im-plies that the upward heat flux should also be nonuniform, thus exerting different effects on sea ice thickness, ice extent, and air-sea heat exchange. The mechanism to generate higher tem-perature in the plateau region was the bypassing of current around the plateau area caused by the special local topography, which restricted water exchange across the plateau and conserved heat in the water body. Second, the deep water down to 1400 m was also warming with a tem-perature increase of 0.2℃. The warming in deep water reflects the occurrence of complicated heat redistribution processes in the intermediate water, which altered the thermal structure in the upper 1400 m. The warming data embody the obvious impact of global climate change on the Arctic Ocean and further studies are wanted.

Reduced Horizontal Sea Surface Temperature Gradients Under Conditions of Clear Skies and Weak Winds

Consideration of the dependence of various components of the sea-surface heat and momentum fluxes on sea surface temperature (SST) leads to an explanation for the observed reduction in the horizontal temperature gradients in the uppermost layer of the ocean (a few to 10 m in depth). Horizontal temperature gradients within the mixed layer can be masked by a near-surface layer of warm water. This camouflage of horizontal temperature gradients has importance for the remote sensing of SST used by the fishing industry, for the estimation of acoustic transmission, and for the forecasting of hurricane development, among many uses of SST data. Diurnal warming conditions in the Straits of Florida are examined by a simulation calculation and by analysis of observations obtained on moorings deployed on the south-east Florida shelf. When there is net heating (i.e., the solar input is stronger than the combined latent, sensible and longwave radiative heat losses) the originally warmer water experiences less heating than the colder water, leading to a weakening of the horizontal SST gradients as seen by surface buoys or satellites. The warmer water also experiences more mixing and therefore less increase in temperature. The strongest effect of the diurnal heating on wind stress occurs when the SST starts out cooler than the air temperature and the atmosphere is stably stratified. Diurnal warming can then rapidly increase the SST above the air temperature because of reduced wind stress and reduced upper-ocean mixing. After that the wind stress increases as convectively driven turbulence contributes to the atmospheric exchange.

The transport of the Weddell Gyre across the Prime Meridian

Abstract Current-meter observations from instruments moored from 1996 to 2001 are used to determine the structure and the volume transport of the Weddell Gyre on the Greenwich Meridian. The record length mean volume transport is 45 Sv to the east within the northern and 56 Sv to the west within the southern limb of the Weddell Gyre. Thus 11 Sv must leave the gyre circulation west of the Greenwich Meridian and enter it east of it. The deficit occurs with 8 Sv mainly in the Circumpolar Deep Water (CDW)/Warm Deep Water (WDW) layer. Surface waters and Weddell Sea Deep Water (WSDW) contribute 2 and 3 Sv, respectively. In contrast to this, 3 Sv more of Weddell Sea Bottom Water (WSBW) flow in the northern limb to the east, than in the southern limb to the west, which suggests a WSBW formation rate of about 3 Sv in the western Weddell Sea. In the Southern Boundary of the Antarctic Circumpolar Current (ACC) a volume transport of 35±16 Sv was found using geostrophic calculations adjusted with two measurements of the absolute velocity. The large heat content of the northern limb points to an extensive heat exchange between the Weddell Sea and the world ocean west of the Prime Meridian. Hence, the heat transport as well as the volume transport suggest that the water masses of the Weddell Gyre are not exclusively replaced in its eastern part, but that there is a significant exchange of water masses to the west of the Prime Meridian.

Upwelling along the western barrier reef of New Caledonia

Temperature decreases of up to 5°C at an automatic station at ~10 m depth at the outer reef of western New Caledonia signalled the occurrence of upwelling. The decreases are related to south-easterly wind events and they can take up to 5 days to develop. Successive wind events can depress the temperature for as much as 1 month. An upwelling shows in thermal satellite imagery as a band of cold water ~10 km wide and as long as several hundred kilometres just outside the reef. The cold water frequently spreads out to sea. The upwellings are more common in summer (October to March) than in winter. During lengthy periods of low wind speeds, the waters outside the reef appear to be overrun by warm water from farther north. The frequent occurrence of the warm water layer in the north may partly explain why upwellings are more common along the southern half of the reef. The entire lagoon cools in winter; most of the lagoon warms in summer, except at the southern end where the waters are cool, perhaps from tidal mixing.

Numerical study on the stability and mixing of vertical round buoyant jet in shallow water

The k-epsilon model was applied to establish the mathematical model of vertical round buoyant jet discharging into confined depth, and it was solved using the Hybrid Finite Analytic Method (HFAM). The numerical predictions demonstrate two generic flow patterns for different jet discharge and environmental parameters: (i) a stable buoyant flow discharge with the mixed fluid leaving the near-field warm in a surface warm water layer; (ii) an unstable buoyant flow discharge with recirculation and re-entrainment of warm water in the near field. Furthermore, the mixing characters of vertical round buoyant jet were numerically predicted. Both the stability criterion and numerical predictions of bulk dilutions are in excellent agreement with Lee and Jirka's experiments and theory.

Late Quaternary paleoceanography deduced from coccolith assemblages in a piston core recovered off the central Japan coast

Nannofossil assemblages from the last 144 ka (∼Marine Isotope Stage, MIS6) were studied in a piston core (MD01-2421) from the NW Pacific (36°01.4′N, 141°46.8′E, WD: 2,224 m), off the coast of central Japan. The site is influenced by both the subtropical Kuroshio and the subarctic Oyashio Currents, and is located just north of the Kuroshio Front. This study attempted to reconstruct paleoceanographic changes in the region by illustrating the past migration patterns of the Kuroshio Current, which is considered to be one of the strongest western boundary currents in the Pacific. In order to reconstruct the past migration patterns of the Kuroshio Current, relative abundance values of several taxa classified as either “Kuroshio Species” or “Oyashio Species” were used as indices. Using these species, a ratio (Tn: Nannofossils temperature index), representing the mixing of the Kuroshio and Oyashio Currents, was calculated to express quantitatively the influence of the Kuroshio Current. Tn values fluctuated widely, ranging from 1.45 (135 ka) to 86.9 (115.3 ka), and corresponds to the warm–cold cycles obtained by oxygen isotope analysis. The fluctuation pattern of percentage abundance of Umbellosphaera spp. shows a strong similarity to that of the precessional cycle. It may indicate that subtropical water has influenced the Japanese coast during these warm intervals, possibly due to the expansion of subtropical divergence. Also, the fluctuation pattern of Tn shows a similar time-transgressive trend to that of the precessional cycle. This implies that latitudinal displacement of the Kuroshio Front was related to subtropical climatic variability. The ratio between Tn and Tp (planktonic foraminifera temperature index) drastically increased at about 20 ka, in MIS2, with small peaks in MIS6. This suggests that a thin layer of warm water may have covered the study area during these intervals. An increased preservation of organic matter (i.e. CaCO 3 preservation) possibly affected the absolute coccolith abundance (coccolith/g dry sediment), although other factors controlling absolute coccolith abundance (e.g. nutrient levels) need to be taken into consideration.

Heat and Mass Budgets of the Warm Upper Layer of the Tropical Atlantic Ocean in 1979–99

Abstract The mass and heat budgets of the warm upper-ocean layer are investigated in the equatorial Atlantic using in situ observations during the period 1979–99, which encompassed a series of warm events in the equatorial Atlantic. The warm water layer is defined as the layer having an in situ temperature higher than 20°C, which is within the core of the equatorial thermocline. The geostrophic transport is calculated by combining gridded temperatures with historical salinity data. The Ekman transport is estimated from observed wind data or model- based wind products. The change in warm water volume is then compared with the horizontal mass convergence, and the residuals are determined. The heat budget of the upper layer is investigated in the same way. Three regions are considered: the equatorial band between 8°N and 8°S to study the meridional redistribution of the warm water and two boxes (western and eastern boxes) to investigate the zonal redistribution of the warm water. Mass and heat budget variabi...

Multiple subsurface phytoplankton blooms occurring simultaneously inthe Skagerrak

he distribution and characteristics of phytoplankton in the Skagerrak in August-September 2000 were analysed in order to evaluate the importance of subsurface phytoplankton peaks to water column ecology and primary production. In areas affected by outflow from the Baltic, enhanced chlorophyll concentrations were found in the warm surface waters (i.e. upper 10-20 m). However, for the central Skagerrak, the major part (50-80%) of the chlorophyll in the water column was found below the warm surface waters. The highest chlorophyll concentrations (up to >18 Mg l -1 ) in the study area were also found below the warm surface waters and up to 95% of total water column primary production was recorded below the warm surface water layer. Measurements of variable fluorescence (F v /F m ) indicated the greatest potential capacity for electron flow in photosystem II in phytoplankton was located below the warm surface waters. Spectrophotometrically determined pigment ratios suggest that the enhanced capacity for photosynthesis in the deeper waters may be related to greater nutrient availability here than in surface waters. Subsurface chlorophyll distributions seen in relation to the different water masses identified in the area, as well as community analysis of the phytoplankton present in the subsurface peaks, indicate the presence of at least three distinct subsurface phytoplankton blooms in the Skagerrak during the study period. Local oxygen saturation maxima recorded immediately above the subsurface peaks provide in situ evidence that these peaks are photosynthetically active. This suggests that new production is taking place in these peaks, although quantification of this production is hampered due to a lack of information concerning the initial conditions in and lifetime of the subsurface peaks. The subsurface phytoplankton peaks were, generally, found immediately above an oxygen minimum that covered the entire study area. In the relatively cold deep Atlantic water found below the oxygen minimum layer, no or very little chlorophyll was recorded and oxygen concentrations increased. Thus, it is argued that the respiration of the organic material produced in the upper part of the water column during late summer may primarily occur in the intermediate layers of the water column.