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Abstract Past studies of noble gas concentrations in the deep ocean have revealed widespread, several percent undersaturation of Ar, Kr, and Xe. However, the physical explanation for these disequilibria remains unclear. To gain insight into undersaturation set by deep‐water formation, we measured heavy noble gas isotope and elemental ratios from the deep North Pacific using a new analytical technique. To our knowledge, these are the first high‐precision seawater profiles of 38Ar/36Ar and Kr and Xe isotope ratios. To interpret isotopic disequilibria, we carried out a suite of laboratory experiments to measure solubility fractionation factors in seawater. In the deep North Pacific, we find undersaturation of heavy‐to‐light Ar and Kr isotope ratios, suggesting an important role for rapid cooling‐driven, diffusive air‐to‐sea gas transport in setting the deep‐ocean undersaturation of heavy noble gases. These isotope ratios represent promising new constraints for quantifying physical air‐sea gas exchange processes, complementing noble gas concentration measurements.

Numerous hydro-acoustic studies of the seabed of the Baltic Sea have revealed the unusual occurrence of sediment contourite drifts and re-suspension at greater water depths. In addition, radiocarbon dating of bulk sediments indicates significant age reversals. We present new geophysical, sediment proxy data (including extensive radiocarbon dating) and hydrographic measurements, which are combined with results of numerous marine geological studies performed during the last decades. These data indicate that a deep-water formation process significantly affected the seabed dynamics during regional climatically cold phases during the last c. 7,000 years. We propose that, during the colder periods (e.g. the Little Ice Age), newly formed bottom waters likely caused widespread re-suspension of organic carbon-rich laminated sediments that were deposited during the preceding warm periods in shallower areas, and this material was transported to and re-deposited in the deeper parts of the Baltic Sea sub-basins. In our scenario, a topographic feature, known as the Baltic Sea Klint, acted as a hydrographic barrier for deep-water formed in the northern Baltic. Thus, during the cold periods increased lateral matter influx from the northern Baltic led to the accumulation of much thicker macroscopically homogenous clayey sediments in sub-basins north of the Klint. Moreover, deep-water formation produced bottom currents that led to the formation of sediment contourite drifts at water depths of >200 m in the Bothnian Sea, the Åland Deep and northern central Baltic Sea sub-basins. Bottom water ventilation in the Baltic Sea is generally assumed to be determined solely by the inflow of oxygen-rich, saline water from the North Sea, but we challenge this assumption and postulate that deep-water formation is a key process that ventilates the bottom waters of the Baltic Sea during climatically cold periods with substantial implications for its sedimentary archive. [ABSTRACT FROM AUTHOR]

Past studies of noble gas concentrations in the deep ocean have revealed widespread, several percent undersaturation of Ar, Kr, and Xe. However, the physical explanation for these disequilibria remains unclear. To gain insight into undersaturation set by deep‐water formation, we measured heavy noble gas isotope and elemental ratios from the deep North Pacific using a new analytical technique. To our knowledge, these are the first high‐precision seawater profiles of 38Ar/36Ar and Kr and Xe isotope ratios. To interpret isotopic disequilibria, we carried out a suite of laboratory experiments to measure solubility fractionation factors in seawater. In the deep North Pacific, we find undersaturation of heavy‐to‐light Ar and Kr isotope ratios, suggesting an important role for rapid cooling‐driven, diffusive air‐to‐sea gas transport in setting the deep‐ocean undersaturation of heavy noble gases. These isotope ratios represent promising new constraints for quantifying physical air‐sea gas exchange processes, complementing noble gas concentration measurements. Plain Language Summary: The deep ocean inherits its dissolved gas content from exchange with the atmosphere at high latitudes and from biological and chemical processes. Noble gases, which are unaffected by biology and chemistry, are useful tools for understanding physical gas exchange. Past observations of dissolved noble gases throughout the deep ocean have revealed that Ar, Kr, and Xe concentrations fall below expected concentrations for water at solubility equilibrium with the atmosphere. However, a physical explanation for this well‐documented undersaturation of noble gases remains unclear. Here we have measured the isotope ratios of Ar, Kr, and Xe in the deep North Pacific as new tools to investigate physical mechanisms of disequilibrium. Our findings suggest that rapid cooling and sinking of surface water at high latitudes, driving air‐to‐sea gas transport with insufficient time for equilibration, is a key process in setting the observed deep‐ocean undersaturation of noble gases. Key Points: Ar, Kr, and Xe isotope ratios were measured in the deep North Pacific to investigate mechanisms of solubility disequilibriumSeawater solubility fractionation factors of heavy noble gas isotope ratios were determined, indicating a weak dependence on salinityObserved isotopic disequilibria point to incomplete cooling‐driven diffusive gas uptake prior to deep‐water formation [ABSTRACT FROM AUTHOR]

Here we investigate the sensitivity of deep-water formation in the north-western Mediterranean Sea to climate variability during the last 2500 yr. With this purpose, the grain-size parameter UP10 (fraction > 10 μm) is used as a proxy for intensity of deep-water circulation. Such a proxy is first validated through the analysis of oceanographic data collected from October 2012 to October 2014 by means of two deep-water mooring lines equipped with sediment traps and currentmeters in the Gulf of Lion and north of Minorca Island. Enhancements of deep current speed resulted from dense shelf water cascading and open-sea deep convection in February 2013 leading to dense-water formation. The grain-size distribution of settling particles from sediment traps collected during 2012–2013 shows a distinctive particle mode and high UP10 values correlated to deep-water formation. These data are consistent with grain-size values in sediment cores from the north of Minorca, thus supporting the validity of the UP10 parameter to reconstruct changes of intensity in deep-water formation and associated near-bottom currents. The deep-water sediment record of the north of Minorca for the last 2.5 kyr shows that the strongest deep-water formation events occurred during relatively warm intervals, such as the Roman Period (123 BCE-470 CE 2 2 BCE: Before Common Era years. CE: Common Era years.), the end of the Medieval Climate Anomaly (900–1275 CE) and the first part of the Little Ice Age (1275–1850 CE). By contrast, our data indicate a progressive reduction in the overturning conditions during the Early Middle Ages (470–900 CE) resulting in weaker deep-water formation events during most of the Medieval Climate Anomaly. Intense deep-water formation events appear to be mostly associated with periods of enhanced Evaporation-Precipitation balance rather than to buoyancy loss due to winter cooling only. Our results suggest that warm sea surface temperature during spring months could have played an important role by increasing the Evaporation–Precipitation balance and favouring buoyany loss by increased of salinity. The comparison our data with other oceanographic and climatic records indicates a change in the proxy relation before and after the Early Middle Ages. Western Mediterranean Deep Water and Levantine Intermediate Water behave in opposite way after the Early Middle Ages, thus indicating that the previously proposed Mediterranean see-saw pattern in the Evaporation-Precipitation balance also influenced convection patterns in the basins during the last 1500 yr. These changes are discussed in the frame of different configurations of the North Atlantic Oscillation and East Atlantic/ West Russian modes of atmospheric variation. • Deep-water formation in the north-western Mediterranean Sea during the last 2.5 kyr. • Grain-size parameter UP10 (fraction > 10 μm): proxy for deep-water circulation. • Validation of the UP10 parameter using present-day data. • Change in the trends before and after the Dark Middle Ages (470–900 year Common Era). • Deep-water formation trends in the Eastern and Western Mediterranean Basins [ABSTRACT FROM AUTHOR]

In the late Miocene, a thick and complex sequence of evaporites was deposited in the Mediterranean Sea during an interruption of normal marine sedimentation known as the Messinian Salinity Crisis. Because the related deposits are mostly hidden from scrutiny in the deep basin, correlation between onshore and offshore sediments is difficult, hampering the development of a comprehensive stratigraphic model. Since the various facies correspond to different salinities of the basin waters, it would help to have physics-based understanding of the spatial distribution of salt concentration. Here, we focus on modelling salinity as a function of depth, i.e., on the stratification of the water column. A box model is set up that includes a simple representation of a haline overturning circulation and of mixing. It is forced by Atlantic exchange and evaporative loss and is used to systematically explore the degree of stratification that results under a wide range of combinations of parameter values. The model demonstrates counterintuitive behaviour close to the saturation of halite. For parameter values that may well be realistic for the Messinian, we show that a significantly stratified Mediterranean water column can be established. In this case, Atlantic connectivity is limited but may be closer to modern magnitudes than previously thought. In addition, a slowing of Mediterranean overturning and a larger deep-water formation region (both in comparison to the present day) are required. Under these conditions, we would expect a longer duration of halite deposition than currently considered in the MSC stratigraphic consensus model. [ABSTRACT FROM AUTHOR]

We analyse a hierarchy of three 1/4° global numerical simulations (ORCA-025.G70 (G70), ORCA-025.G85 (G85) and GLORYS1V1 (GLORYS)) by assessing their performance against observational data in the western Mediterranean. When compared with the EN3_v2a temperature and salinity database, the simulations are capable of reproducing surface layer temperature interannual variability but G70 is inaccurate with intermediate and deep-layer trends. This aspect is improved by the increased vertical resolution of G85 and by data assimilation in GLORYS. Salinity is the most problematic parameter because of the imbalance of the freshwater budget derived from inaccuracies in the atmospheric forcing parameters. Surface salinity restoring is needed in order to avoid salinity drift and inaccurate sea-level trends. G70, with a stronger relaxation, has a lower trend closer to altimetric measurements than G85. Mean surface circulation is well reproduced for relatively large-scale signals. We further show that G85 and GLORYS provide evidence of the 2004-2005 and 2005-2006 deep convection events in the Gulf of Lion. Finally, transports through the main straits of the western Mediterranean are correct in order of magnitude, direction and seasonal cycle when compared with observations. This study contributes to the improvement of the ORCA hierarchy of simulations and points out the strengths and weaknesses of these simulations in the Mediterranean Sea.

Deep-water formation (DWF) in the East Sea (Japan Sea) can affect the regional meridional overturning circulation via air–sea interactions. Thus, it is important to monitor long-term changes to understand the future regional climate and, thus, marine ecosystem changes associated with DWF. In this study, we propose a new DWF estimation method based on satellite measurements rather than on sparse in situ measurements. First, we estimated the volume of the mixed water (V MW) as a proxy for the intensity of the DWF based on the HYbrid Coordinate Ocean Model (HYCOM) data and examined the V MW signals in satellite measurements of the chlorophyll- a (Chl- a) concentrations and sea-level anomalies (SLA) from January to March for 21 years (1998–2018). When the DWF was intense in the East Sea, Chl- a and SLA decreased. This inverse relationship between the DWF and sea-surface features was much clearer during strong DWF years than during weak DWF years. The decreasing rates of Chl- a and SLA over strong DWF years were −0.0044 mg m−3 and −0.0020 m day−1, respectively. Furthermore, we estimated the V MW from the SLA and Chl- a using a multi-linear regression. These findings will allow us to understand the intensity of the DWF through V MW using multi-satellite measurements alone. • Satellite sea level height and Chlorophyll a concentration can be used to estimate deep water formation in the East Sea (Japan Sea). • The period of DWF in strong DWF years was 32 days on average, whereas that in weak DWF years was 12 days. • During strong DWF years, while the Chl- a trend showed a significant negative trend (−0.0044 mg m−3 day−1), the decreasing SLA trend(−0.0022 m day−1) was compared to the trend of 21-year climatology. • If both Chl- a and SLA show a negative trend, the year shows high potential, being classified as a strong DWF year. • The decreasing rates in Chl- a and SLA as MLD deepenes were -3x10−4 mg m−3 m−1 and -1x10−4 m m−1, respectively. [ABSTRACT FROM AUTHOR]

In the Mediterranean, blue whiting, Micromesistius poutassou, constitutes a traditional fisheries resource. Over several decades, blue whiting landings in the Catalan coast (northwestern Mediterranean) have displayed cyclical variations, of c. 6 yrs, slightly decreased to five in the last two decades, as shown through wavelet analysis. These fluctuations have persisted under very different levels of fishing effort. This study evaluates the hypothesis that deep-water formation in the adjacent Gulf of Lions, and the enhanced primary productivity related to it, determines recruitment strength in blue whiting that results ultimately in the observed periodicity of the blue whiting landings. The link between landings and environmental drivers was explored using lagged cross-correlations, with 0- and 1-yr lag. The variables considered included large-scale indices [North Atlantic Oscillation (NAO) and the Atlantic Multi-decadal Oscillation (AMO)], Mediterranean climate indices [MO and Western Mediterranean Oscillation (WeMO)], and variables defining the local environmental conditions in the northwestern Mediterranean (sea-air heat flux, winter air temperature anomaly and Rhône river runoff). Significant correlations were only found between landings (1961-2011) and sea-air heat flux, which is generally taken as an indicator of processes of deep water convection, at 0 and 1-yr lag. These results suggest that the observed fluctuations in blue whiting landings respond to oceanographic processes taking place in the Gulf of Lions. [ABSTRACT FROM AUTHOR]

Water mass characteristics and circulation patterns in the Gulf of Aqaba and northern Red Sea were studied for the first time during the r/v "Meteor" cruise leg 44/2 from February 21st to March 7th 1999 using temperature-salinity profiles and current observations. The deep water in the northern Red Sea had similar characteristics to the well-mixed upper 450 m of water in the Gulf of Aqaba. This indicates that the winter mixed waters of the Gulf of Aqaba contribute significantly to deep-water in the northern Red Sea. Mixing in the Gulf of Aqaba is an annually repeated event that starts with the cooling of the surface water during November-December and reaches a maximum, which in most years extends down the entire water column in March-April. Waters deeper than the mixed layer in the Gulf seems to be rather passive and play no specific role in water mass formation in the northern Red Sea. In contrast to the Gulf of Aqaba, the upper 200 m of the northern Red Sea were stratified (21.5-23.5oC, and 40.0-40.3 PSU). Stratification at the Strait of Tiran was weak (21.6-22.0oC, and 40.3-40.5 PSU) and disappeared abruptly in the Gulf of Aqaba (21.4-21.6oC, and 40.6-40.7 PSU). A well-developed cyclonic gyre with a diameter of about 50-60 km and maximum velocity of about 0.4 m s-1 was observed in the stratified upper 200 m of the northern Red Sea waters. The gyre may contribute to the preconditioning for intermediate water formation in the northern Red Sea.

Abstract: Interrannual variability in the surface and intermediate water masses of the North–Central Aegean Sea is being investigated through data collected by the Hellenic Navy Hydrographic Service (HNHS) during the Eastern Mediterranean Transient (EMT) post-peak period. Data suggest that following the last major deep-water formation episode in the Aegean Sea (1993), Black Sea Water (BSW) is confined to the northernmost part of the basin, while saline Levantine Surface Water (LSW) becomes the dominant Central Aegean surface water mass, intruding below the BSW layer even north of Lemnos Island. Furthermore, highly saline intermediate masses transfer additional salt to the North–Central Aegean basin. After the early 90s, BSW gradually reclaims most of the Central Aegean while the salinity of both LSW and intermediate masses is reduced. The enhanced presence of these highly saline water masses in the early 90s, presumably signifies the intrusion of high salinity water of Levantine origin into the North–Central Aegean following the massive outflow of dense Aegean water into the Eastern Mediterranean. This salinity intrusion was one of the preconditioning factors that enhanced dense water formation in the Aegean during the last major deep-water formation phase of the EMT, affecting the characteristics of the deep-water masses produced. [Copyright &y& Elsevier]

Abstract: Icebergs are an important part of the fresh-water cycle and, until now, have not been explicitly represented in Intergovernmental Panel on Climate Change (IPCC) class coupled global circulation models (CGCMs) of the climate system. In this study we examine the impact of introducing interactive icebergs in a next-generation CGCM designed for 21st Century climate predictions. The frozen fresh-water discharge from land is used as calving to create icebergs in the coupled system which are then free to evolve and interact with the sea-ice and ocean components. Icebergs are fully prognostic, represented as point particles and evolve according to momentum and mass balance equations. About 100,000 individual particles are present at any time in the simulations but represent many more icebergs through a clustering approach. The various finite sizes of icebergs, which are prescribed by a statistical distribution at the calving points, lead to a finite life-time of icebergs ranging from weeks, for the smallest icebergs (60m length), up to years for the largest (2.2km length). The resulting melt water distribution seen by the ocean enhances deep-water formation, in particular on the continental shelves, relative to the model without icebergs. [Copyright &y& Elsevier]

Abstract: Simulations of the interannual variability of the deep-water formation processes in the Adriatic basin for the years 1979–1999 are performed using the Princeton Ocean Model (POM) with a ∼10km grid and 6-h atmospheric forcing provided by the European Center for Medium Weather Forecast (ECMWF). Focus is given to the pattern and amplitude of the interannual variability of the water mass formation processes in terms of deep-water formation sites, rates and characteristics. The connection of this variability with the interannual variability of (a) the atmospheric forcing and (b) the open boundary characteristics is investigated. The model performance is tested against the few available observations of deep-water formation processes inside the basin and generally shows a good agreement with the main characteristics of the mixed layer and the deep-water formation rates. A strong interannual variability is found in the calculated deep-water formation rate of the basin, which is highly dependent on the interannual variability of the atmospheric forcing. This rate becomes three times larger than climatology during the biennium 1992–1993, and during all years it is associated mostly with the events of enhanced buoyancy loss and not with the mean winter buoyancy fields. Advection through the open boundary plays an important role in determining the characteristics and volume of deep water formed inside the Adriatic basin, but it is the high frequency atmospheric forcing that determines the amplitude of the interannual variability of deep-water formation rates. [Copyright &y& Elsevier]

Planktic and benthic foraminifera assemblages from a set of sediment cores, collected on the Adriatic shelf and the Southern Adriatic deep basin, provide compelling evidence of submillennial-scale environmental changes during the last 6000 years. Repeated peaks in Globigerinoides sacculifer represent warm-dry intervals, including the 'Mediaeval Warm Period', the 'Roman Age', the late 'Bronze Age' and the 'Copper Age'. The Last Occurrence (LO) of G. sacculifer (550 years BP) approximates the base of the 'Little Ice Age' (LIA). Significant turnovers in the structure of the water column reflect changes in the rate of formation and depth of flow of the North Adriatic Dense Water (NAdDW) and the Levantine Intermediate Water (LIW). About 7500 years BP the benthic oxygen isotope records mark the timing when the NAdDW formation intensified on the slope and shifted to its modern route. About 5500 years BP, when sea level reached its modern high stand, oxygen isotope records of intermediate planktic dwellers indicate a northward intrusion of the LIW on the slope. The oscillating isotope trends during the last five millennia document a discontinuous invasion of LIW into the Central Adriatic, possibly reflecting short-term climate changes with weakened LIW production during colder and wetter intervals. [ABSTRACT FROM AUTHOR]

Abstract: We present high-precision measurements by a new isotope dilution technique of a suite of inert gases in the North Pacific. Remarkably smooth gradients in Ar, Kr and Xe from near equilibrium in intermediate waters to several percent undersaturated in deep waters were observed. The general pattern in the deepest waters was that Ar, Kr and Xe were undersaturated (Ar least and Xe most), while N2 was close to equilibrium, and Ne was supersaturated. We propose that this pattern was produced by the interaction between the different physical properties of the gases (solubility and the temperature dependence of solubility) with the rapid cooling and high wind speeds that characterize deep-water formation regions. In a simple model of deep-water formation by convection, the saturations of the more temperature-sensitive gases were quickly driven down by rapid cooling and could not reequilibrate with the atmosphere before the end of the winter. In contrast, the gas exchange rate of the more bubble-sensitive gases (Ne and N2) was able to meet or exceed the drawdown by cooling. Our simple convection model demonstrates that the heavier noble gases (Ar, Kr and Xe) are sensitive on seasonal timescales to the competing effects of cooling and air–sea gas exchange that are also important to setting the concentration of CO2 in newly formed waters. [Copyright &y& Elsevier]

Hydrographic, oxygen and nutrient data collected in the Nordic Seas during the 1990s are presented. During the decade, deep waters originating from the Arctic Ocean, identified by salinities in excess of 34.9, spread into the Greenland Basin. In 1991, these waters extended westward from the mid-ocean ridge to about 2°E. This process continued over time and by 1993 there was a layer with salinities above 34.9 along the entire section, between 7.6°W and the Barents Sea Slope, and probably across the whole basin. In 2000 the basin had these high salinities at depths greater than 1400 m. At 1500 m in the central basin the salinity increase during the decade was 0.012 units, decreasing to 0.006 at 3000 m, and associated temperatures increased by 0.28 and 0.09°C, respectively. This warming more than compensated for the salinity increase so that the density of the deep water decreased during the decade, σ3 decreasing by 0.027 kg m-3 at 1500 m and by 0.006 kg m-3 at 3000 m. Decreasing oxygen content and increasing concentrations of silicate further indicated the increasing influence of Arctic Ocean Deep Water. Interaction with the atmosphere is decisive for the conditions in the area. In the central Greenland Sea there is close correlation between wind forcing and upper-layer salinity. Significant deep-water formation occurs only during cold winters, or rather, in periods with several succeeding cold winters and the 1960s were the first period in which these conditions occurred since 1920. This is shown by meteorological observations at Jan Mayen since 1921, and at Stykkisholmur, Iceland, since 1823. Relatively high salinities were observed near the bottom over the Iceland Plateau. These waters seem to be derived from Arctic Ocean deep waters that have been diverted from the East Greenland Current, into the East Icelandic Current. While flowing through the Iceland Sea their nutrient concentration increases considerably. This water flows into the Norwegian Basin where it forms a slight salinity maximum around 1500 m, which is associated with a minimum in oxygen content. At greater depths the water masses are from the Greenland Sea. The salinity decreases and the oxygen increases toward approximately 2500 m, from where the trends are reversed toward a slight salinity maximum around 3000 m, where there also is a minimum in oxygen as well as in CFC-11. These characteristics seem to derive from Arctic Ocean Deep Water, floating above waters more characterized by Greenland Sea Bottom water nearest to the bottom as suggested by decreasing salinity and an increase in both oxygen and CFC-11 concentration. This shows that even the very homogeneous Norwegian Sea Deep Water is stratified. There are also slight differences between the deep waters of the basins in the Norwegian Sea. In the Norwegian Basin the deep water has slightly higher salinity, lower dissolved oxygen and higher silicates than the deep water in the Lofoten Basin, and even more so compared with the area west of Bear Island. This shows that the Lofoten Basin and the northern Norwegian Sea are more directly influenced by waters from the Greenland Sea than the Norwegian Basin. [Copyright &y& Elsevier]

General circulation and deep-water formation (DWF) processes in the Adriatic basin in a climatological year were numerically simulated in a high-resolution (1/20th of a degree) implementation of the Princeton Ocean Model (POM). The “perpetual” year atmospheric data were computed from the ECMWF Reanalysis data (1°×1°) covering the period 1979–1994. The model reproduces the main basin features of the general circulation, water mass distribution and their seasonal variability. The Adriatic Deep Water exiting through the Otranto Strait is produced with two different mechanisms inside the basin: (a) by open ocean deep convection over the Southern Adriatic Pit and Middle Adriatic Pit (b) on the continental shelf of the Northern and Middle Adriatic. The estimated contributions of both mechanisms suggest that 82% of the Adriatic Deep Water is formed inside the Southern Adriatic Pit, while all the higher density water in this water mass comes from the northern regions. The role of mesoscale eddies at the periphery of the dense-water chimney in the Southern Adriatic Pit was examined and their contribution to the lateral buoyancy flux, during the convection process, found to be small. The DWF rate at Otranto Strait is 0.28 Sv with σθ over 29.15. The sensitivity of the DWF processes to interannual variability of the buoyancy forcing and river runoff was assessed with a number of process-study numerical experiments. In these experiments the effect of an imposed “extreme” buoyancy forcing during 1 year, on the DWF rates, was to modify them during the specific year, but the effects were still present in the following normal climatological year. This shows that the DWF rates and their mass characteristics at a specific year depend not only on the atmospheric conditions prevailing that specific year but on the previous year''s as well, thus leading to the concept of a “memory” of the basin. [Copyright &y& Elsevier]

The Labrador Sea is a major sink of anthropogenic CO2 due to deep-water formation in winter. To investigate the relative importance of different forms of export flux, we used a physical-biogeochemical model to simulate the vertical fluxes of particulate and dissolved biogenic carbon as a function of winter convection, food web dynamics and zooplankton vertical migration. The C:N ratio of these export fluxes was simulated based on trophic dynamics and bacterial activity. The model was run using winter convection and seasonal mixed layer evolution extracted from multi-year physical data collected in the central Labrador Sea. Comparisons between model output and data from the Labrador Sea and other systems indicate that the model provides a realistic picture of carbon and nitrogen pools and fluxes. Our results suggest that on an annual basis, dissolved organic carbon (DOC) export by deep, vertical convection is greater than that of the sinking flux of POC. Furthermore, the C:N ratio of exported dissolved organic matter (DOM) is higher than that of the particle sinking flux, resulting in 23% more carbon exported than would be estimated if predictions were made from the Redfield ratio (e.g., 11.4 vs. 7.0 for DOM and particulate organic matter, respectively, at the bottom of the euphotic zone and 17.2 vs. 9.3 at 1000 m depth). The active export of carbon by the respiration and mortality of migrating zooplankton amounts to 19% of sinking flux annually, but only 6% of total carbon export because of the high rates of DOC export in deep-water formation regions. Our model simulations indicate that non-Redfield ratio DOC export characterizes the function of the biological pump in deep-water formation regions. [Copyright &y& Elsevier]

The Eastern Mediterranean Transient (EMT) was the major climatic event in the circulation and water mass properties of the Mediterranean in the last century. In this paper, we describe the present status of the EMT and its evolution since 1995 using hydrological and tracer data from 1997 to 1999. Few but important changes have been observed in the circulation pattern. The intrusion of the Asia Minor Current (AMC) that carries the saline Surface Levantine Waters into the Aegean has been reduced compared to the picture of late 1980s. This means that one of the mechanisms that increased the salt content of the Aegean during the peak of the EMT is no longer present. The Modified Atlantic Water (MAW) signal that has been weakened in the Levantine Basin during the early stages of the EMT has also been re-enhanced. The Aegean still functions as a source of deep (Cretan Deep Water, CDW) and intermediate waters (Cretan Intermediate Water, CIW) for the Eastern Mediterranean, although with modified characteristics. The most important changes in the thermohaline structure of the Cretan Sea (southern Aegean Sea) are the weakening of the signal of the old Mediterranean mid-depth waters and the modification of the properties of the CDW both leading to a reduced stratification. The outflowing CDW is no longer dense enough to reach the bottom of the adjacent basins, but ventilates layers between 1500 and 2500 m. Only the deep eastern Straits of the Cretan Arc are still active in the discharge of CDW, while at the western Strait (Antikithira), the density of the outflowing water was reduced significantly. The intermediate water CIW formed in the Aegean is characterized as a shallow CFC-12, temperature and salinity maximum layer, and differs much from the “old” CIW formed before the EMT, which was found in the layer below the Levantine Intermediate Water (LIW). The new CIW extends into the Ionian Basin through Antikithira Strait. It has lately been observed to enter the Adriatic, where its high salinity is expected to re-establish deep-water formation in this basin. The spreading of the CDW that had been deposited in the Cretan Passage in the first phase of the EMT has progressed further. The entire bottom layer of the Levantine Basin is now covered by the CDW. In the Ionian, the CDW has reached the Straits of Sicily and Otranto. Similar pathways in the Ionian are followed by the new shallower outflow of the CDW. [Copyright &y& Elsevier]

Carbonate preservation records from a number of drill sites in the North Atlantic and adjacent Norwegian–Greenland Sea (NGS) are used to reconstruct variations in North Atlantic Deep Water (NADW) production over the past 3 Myr. Before the initiation of major Northern Hemisphere glaciation, good carbonate preservation was recorded in the North Atlantic and the NGS supporting the superconveyor model of accelerated NADW formation in the late Pliocene. After the inception of main Northern Hemisphere glaciation, NADW formation in the NGS was blocked-off during the period 2.8–1.9 Ma. Carbonate was only badly preserved due to (1) low production of carbonate shells in surface waters, (2) sluggish renewal of deep waters induced by a rather stable sea-ice cover, and/or (3) production of carbonate-corrosive dense brines during sea-ice formation (e.g. sea ice dissolution mode). In contrast, contemporaneous good preservation in the adjacent North Atlantic indicates efficient NADW production. During the middle Matuyama (1.9–1.4 Ma), the first intrusions of the Proto-Norwegian Current into a narrow corridor in the southeastern NGS are evidenced by much better carbonate preservation. A decrease both in carbonate content and preservation towards the north and west of this corridor indicates the proximity of the polar front and gives evidence that NADW production was efficiently triggered by the Atlantic water entrainment mode. During the past 1.2 Myr carbonate preservation patterns in the NGS clearly reflect major global events like the Mid-Pleistocene Transition and the mid-Brunhes dissolution event. The onset of the Mid-Pleistocene Transition at 1.2 Ma is characterized by a complete shift to higher carbonate contents in the southeastern NGS and Labrador Sea. Overall, good preservation during both interglacials and glacials is only interrupted by high-frequency, short-term dissolution spikes, which were induced by ice sheet collapse and development of extensive meltwater lids. As a consequence, NADW was produced nearly continuously during glacials in the Nordic Seas. However, due to its lower density it was entrained into intermediate water levels in the North Atlantic and, thus, enforced the intermediate water circulation loop, whereas a decrease in lower-NADW production is observed contemporaneously. [Copyright &y& Elsevier]

The outer Ross Sea continental shelf has experienced large variations in ice sheet extent over the Pleistocene that are theorized to be largely driven by changes in the westward-flowing Antarctic Slope Current (ASC) at the continental shelf break. This current regulates southward incursions of warm modified Circumpolar Water, and it is thought to have triggered past marine ice sheet retreat. Additionally, expansions of grounded ice sheets on the continental shelf have fundamentally altered the Ross Sea water mass formation processes, influencing surface water salinity, sea ice cover, nutrient utilization, deep-water ventilation, and primary productivity. Here, we report the geochemical, physical properties, grain size, bulk δ15N, and diatom records during the late Pleistocene from two sediment cores from the Iselin Bank on the outermost continental shelf in the Ross Sea. These core sites were not overridden by grounded ice sheets during the late Pleistocene glacial-interglacial cycles, allowing for a continuous archive of glacimarine environments that were influenced by the ASC. Interglacial periods are typically characterized by high surface water productivity and nutrient utilization, with Chaetoceros resting spores indicating nutrient limitation under open ocean conditions, and glacial periods are typically characterized by low surface water productivity and nutrient utilization, with sea ice diatoms and planktonic foraminifers indicating light limitation under extensive sea ice/ice margin proximal conditions. A grain size analysis indicates coarse-skewed distributions and winnowing in the Iselin Bank region during cold periods. The winnowing may be related to enhanced ASC flow instead of density driven shelf water outflow. [ABSTRACT FROM AUTHOR]

The ocean surface rapidly exchanges heat, freshwater, and gases with the atmosphere, but once water sinks into the ocean interior, the inherited properties of seawater are closely conserved. Previous water-mass decompositions have described the oceanic interior as being filled by just a few different property combinations, or water masses. Here we apply a new inversion technique to climatological tracer distributions to find the pathways by which the ocean is filled from over 10,000 surface regions, based on the discretization of the ocean surface at 2° by 2° resolution. The volume of water originating from each surface location is quantified in a global framework, and can be summarized by the estimate that 15% of the surface area fills 85% of the ocean interior volume. Ranked from largest to smallest, the volume contributions scaled by surface area follow a power-law distribution with an exponent of −1.09 ± 0.03 that appears indicative of the advective-diffusive filling characteristics of the ocean circulation, as demonstrated using a simple model. This work quantifies the connection between the surface and interior ocean, allowing insight into ocean composition, atmosphere-ocean interaction, and the transient response of the ocean to a changing climate., Earth and Planetary Sciences