Saline Deep Water Research Articles

Sedimentation and Pelagic Retention of Particulate C, N and P in the Coastal Northern Baltic Sea

Sedimentation and pelagic retention capacity of particulate carbon, nitrogen and phosphorus as well as the impact of resuspension and preservation on sedimentation rates were studied during spring and summer in the SW coast of Finland, Baltic Sea. Formaldehyde preservation resulted in significantly higher carbon, nitrogen and chlorophyllasedimentation rates when compared to traps without preservative. This was mainly attributable to contamination by vertically migrating micro-organisms in traps with formaldehyde and mineralization inside the non-preserved trap cylinders. During the spring bloom, stoichiometric ratios of settled and suspended particulate material indicated that phosphorus was retained in the pelagic system almost twice as effectively as carbon and nitrogen, while carbon and nitrogen were settling at equal rates. During summer, when sedimentation rates were low, nutrient ratios of settled and suspended matter indicated that both N and P were recirculated in the pelagic system more effectively than carbon while P was retained 1·4 times more effectively than nitrogen. High current velocities and increase of deep-water salinity correlated with increased sedimentation of particulate material, with low N:P, C:P and high C:N ratios indicating input of resuspended phosphorus during upwelling events. Wind velocity and direction did not have any clear relationship to the quality of settled material, denoting that wind-induced wave action and transport of littoral material had minor impact on sedimentation rates. Primary sedimentation of carbon corresponded to 57% of the total primary production during the study period from April to August, while that of nitrogen was 42% of estimated nitrogen assimilation, indicating that the overall export of carbon was more effective than that of nitrogen from the pelagic system.

Abstract: Sources of Hydrocarbon-Rich Fluids Advecting on the Seafloor in the Northern Gulf Of Mexico

ABSTRACT Pore fluids associated with hydrocarbon seeps in deepwater Gulf of Mexico were sampled and analyzed for chemical and isotope compositions in order to determine their nature and origin. Three types of fluids have been discerned. Fluids pertaining to type I have normal Gulf of Mexico deepwater salinities (about 38) and their 87Sr/86Sr ratios (0.70916, n=3) are identical to the overlying seawater (0.70917). These fluids originated as seawater trapped in the sediments whose chemical and isotope compositions were modified by microbial sulfate reduction, authigenic carbonate precipitation and gas hydrate sublimation. Fluids of the second type are highly saline (116 to 182 salinity range), with 87Sr/86Sr ratios (0.70797 to 0.70897, n=3) below that of seawater and elemental chemistry compatible with halite dissolution. This type of fluids is interpreted to be derived by dissolution of shallow subsurface salt diapirs during seawater convective circulation. The third type fluids are characterized by high salinity (range from 52 to 155), high concentrations of Ba, Sr and Ca and lower than seawater 87Sr/86Sr ratios (0.70843 to 0.70862, n=8). These fluids are likely to be derived from deep-seated formation waters advecting on the seafloor. Whereas the first and second type of fluids occur in authigenic carbonate deposition areas, the third type is exclusively encountered in barite deposition sites.

Late Quaternary paleoceanographic changes in Dixon Entrance, Northwest British Columbia, Canada; evidence from the foraminiferal faunal succession

Late glacial and Holocene foraminiferal stratigraphy of 7 piston cores from Dixon Entrance on the Pacific coast of Canada yielded 11 biofacies defined in part by cluster analysis and in part by the percentage of temperate species. Temperate species are defined as those that are not reported to be Living north of the southern Bering Sea. It is possible to define three phases in the latest Wisconsinan deglaciation based on the percentage of temperate species: the glacial phase with 0 to 5% temperate species, the transitional phase with 5 to 20%, and the temperate phase with more than 20%. Assemblages dominated by Epistominella vitrea and Cassidulina reniforme characterize the oldest, “glacial” deposits (14,000-12,900 BP). Younger sediments have suhstrateinfluenced assemblages. Muddy “transitional” deposits (12,900-10,500 BP) are dominated by the same species as the glacial material, but the coarser sediments are dominated by the attached form Lobatulafletcheri. The most abundant species in muddy “temperate” deposits (<lo500 BP) is either Epistominella paciJca or Nonionella stella. Coarse sediments of the same age are numerically dominated L. Jletchen; and also contain temperate species of the genus lslandiek. Compared to Queen Charlotte Sound further south, Dixon Entrance had generally more open marine conditions due in part to the greater depth that facilitated shoreward advection of wanner and more saline deep waters as part of an intense estuarine circulation driven by glacial melt.

A laboratory study of the effect of frost flowers on C band radar backscatter from sea ice

C band images of Arctic sea ice taken by the ERS 1 synthetic aperture radar show transitory regions of enhanced radar backscatter from young sea ice. Published field observations associate this increase with frost flower growth and the capture of blowing snow by the flowers. To investigate the first part of this phenomenon, we carried out a laboratory experiment on the response of C band radar backscatter to frost flowers growing on the surface of newly formed saline ice. The experiment took place in a 5 m by 7 m by 1.2 m deep saline water pool located in a two‐story indoor refrigerated facility at the Cold Regions Research and Engineering Laboratory. Sodium chloride ice was grown in this pool at an air temperature of −28°C. The frost flowers first appeared on the ice surface as dendrites and then changed to needles as the ice sheet grew thicker and the surface temperatures became colder. The frost flowers reached to a height of 10–15 mm, and beneath each cluster of frost flowers a slush layer formed to a thickness of approximately 4 mm. Far‐field radar measurements of the backscatter from the ice were made at incident angles from 20° to 40° and at approximately 6‐hour intervals throughout the 3‐day period of the experiment. A backscatter minimum occurred early in the flower growth at the time coincident with an abrupt doubling in the ice surface salinity. Once the full flower coverage was achieved, we removed first the crystal flowers and then the slush layer from the ice surface. The results for these cases show that the crystals have little impact on the backscatter, while the underlying slush patches yield a backscatter increase of 3–5 dB over that of bare ice. The laboratory results suggest that this relative backscatter increase of approximately 5 dB can be used as an index to mark the full areal coverage of frost flowers.

Latest Paleocene benthic foraminiferal extinction and environmental changes at Tawanui, New Zealand

A major extinction of intermediate‐water (500–1000 m) benthic foraminiferal species coincided with a major decrease in δ13C (2.8‰) of terrestrial organic matter (n‐C29 alkane) and δ34S (20‰) of whole rock sulfide in a continuous siltstone sequence in the Tawanui Section (46°S paleolatitude) along the Akitio River, southeastern North Island, New Zealand, in the middle part of the uppermost Paleocene nannofossil zone (CP8). The benthic extinction (25% of species) occurred over ∼3 kyr at ∼55.5 Ma. Increases in kaolinite/illite and kaolinite/smectite ratios and in terrestrial organic carbon percentages started ∼3 kyr before the major benthic extinctions, lasted over ∼40 kyr, and probably reflect warmer climate and increased rainfall. The productivity of planktonic foraminifera and calcareous nannoplankton decreased ∼3 kyr prior to the major extinctions and recovered at the time of benthic extinctions. These events that started ∼3 kyr before the extinction can be best explained by warming, increased rainfall, reduced salinity of surface waters, and increased influence of warm saline deep water (WSDW). Benthic foraminiferal oxygen indices indicate a strong decrease in dissolved oxygen levels within the intermediate water from low oxic (1.5–3.0 mL/L O2) to suboxic (0.3–1.5 mL/L O2) conditions coinciding with the benthic extinctions. Increases in total organic carbon (TOC) and in the hydrocarbon‐generating potential of kerogen (measured as the hydrogen index (HI)) agree with the interpretation of decreased dissolved oxygen levels of the intermediate water. The lowest oxygen conditions lasted ∼40 kyr and coincided with a decrease in calcareous benthic foraminiferal productivity, highest TOC levels, and lowest δ13C of terrestrial organic carbon. Dominant formation of WSDW or sluggish intermediate‐water circulation caused by warming and high rainfall in high‐latitude areas most likely led to the ∼3‐kyr time lag between events on land and in surface waters preceeding the extinction and the development of dysaerobia in the sea, coinciding with the major benthic extinction and decrease in δ13C and δ34S in New Zealand. Global warming of deep and intermediate waters may have caused decomposition of methane hydrate in sediments, resulting in a strongly decreased δ13C of marine carbonates, promoting dysaerobia in the ocean, and warming global climate by increased methane concentrations in the atmosphere. Upwelling of WSDW, occurring soon after it became dominant in high‐latitude areas, is likely responsible for the recovery of normal salinity and the concomitant recovery of planktonic foraminifera and calcareous nannoplankton productivity in high‐latitude surface waters. Minor benthic foraminiferal extinctions (9% of species) occurred ∼40 kyr after the major extinctions, lasted ≤ ∼6 kyr, and coincided with the initiation of environmental recovery.

The Eocene-oligocene preglacial-glacial transition in the atlantic sector of the Southern Ocean (ODP site 690)

High resolution interdisciplinary analyses of the clay and coarse (>40 μm) fractions of ODP Leg 113 Site 690 Eocene-Oligocene sediments on the flank of the Maud Rise, provide information on paleoproductivity, water masses, paleoclimate and erosion in the Antarctic range as well as on the cyclicity of these processes. Three time intervals are distinguished: 1. (1) The middle Eocene, characterized by (a) nearly pure smectites, (b) productivity varying between relatively high values in the 42–44 Ma interval to very low values after 42 Ma, and (c) cyclic variations which correspond to changes in clay mineral associations. A warm saline deep water mass is inferred to have protected carbonate shells against dissolution at Site 690. We interpret the abundant mica in the coarse fraction as distributed by intermediate currents. 2. (2) The latest middle Eocene-late Eocene, characterized by low productivity values increasing with time. Kaolinite and illite concentrations also increase. Since the middle/late Eocene boundary mixing in the water column, which starts during a cooling event, causes similar clay mineral assemblages at Site 690 and at Site 689 on top of Maud Rise. 3. (3) The Oligocene, separated from the Eocene by a hiatus, is characterized by high productivity, highly increased amounts of illite and other minerals originating from erosion and physical weathering of Antarctica, and by cyclic variations of clay mineral indices which appear to be synchronous with productivity variations with a 400–450 kyr cyclicity. Six periods of strong carbonate dissolution associated with low productivity levels are attributed to incursions of cold carbonate aggressive bottom water of a “Proto-AABW” type.

Implications for the creation of warm saline deep water: Late Paleocene reconstructions and global climate model simulations

A global warming trend began during the late Paleocene that culminated in the early Eocene with the highest global temperatures of the Cenozoic. We have reconstructed late Paleocene surficial boundary conditions and modeled atmospheric conditions using the Goddard Institute for Space Studies general circulation model version II (GISS GCM II). These experiments were conducted to test the hypothesis that warm saline deep water formed during the late Paleocene and to understand atmospheric circulation near the beginning of a period of global warming. The warming is attributed primarily to increased sea surface temperatures at high latitudes. The sensitivity of the climate to ocean temperature was tested using two sea surface temperature distributions, each delimited latitudinally by oxygen isotope values, but with different east-west gradients. The simulations discussed here contain several features unique among warm climate experiments. The first experiment (P-1) used latitudinally constant (zonal) sea surface temperatures. The zonally distributed sea surface temperatures strengthen the general circulation of the atmosphere. In particular, Hadley Cell circulation is intensified, leading to extremes of precipitation in the equatorial region and extreme evaporation across subtropical oceans. The unusual results prompted a second experiment with modern east-west sea surface temperature gradients superimposed and referred to as P-Gradient (P-Grad). The east-west gradients in the sea surface temperature field exert a strong influence on the general atmospheric circulation, but the extreme zonality prevails. Under extreme zonal conditions it is possible to create a model where evaporation is in excess of precipitation by as much as 3 mm/day. If this occurred in restricted areas in a generally warmer ocean, such as the late Paleocene eastern Tethys Ocean and parts of the South Atlantic Ocean, it should be possible to create very saline water, which could become a component in warm saline deep water formation.

Late Eocene-Oligocene paleoceanography in the southern Indian Ocean (ODP Site 744)

The late Eocene through Oligocene changes in the paleoceanography of the southernmost Indian Ocean have been reconstructed by means of a coarse fraction analysis of closely spaced samples (20 cm = about 20 kyr) from ODP Site 744, Kerguelen Plateau. Surface water productivity, reconstructed from accumulation rates of opal skeletons and benthic foraminifers is low in the early late Eocene, increases at about 36 Ma and shows a sharp increase to maximum values in the earliest Oligocene. In the early late Oligocene it decreases gradually to a minimum and increases again to a maximum in the latest Oligocene. Beside this general trend productivity varies in short-term cycles of a duration of about 400 kyr (340 kyr in the latest Oligocene) with maxima in productivity in warmer Oligocene periods. These productivity variations are reflected by strong variations in carbonate dissolution. Changes in bottom water mass chemistry have been deduced from the degree of carbonate dissolution and it's relation to productivity proxies. Following Kennett and Stott (1990), it is suggested that a proto-antarctic bottom water (proto-AABW) and an overlying warm, saline deep water (WSDW) from low latitudes shifted vertically and latitudinally with time and exerted their influence on the sediments of Site 744. Proto-AABW is detected by means of strong carbonate dissolution when productivity is low. WSDW is detected by means of an excellent carbonate preservation despite high productivity. Terrigenous material occurs as very coarse ice-rafted detritus (IRD) in the late Eocene (167–168.5 mbsf) and after a main shift in oxygen isotopes in the early Oligocene. Very low amounts of 40–125 μm sized mica and very few quartz grains occur only in high productivity periods and at the transition from low to high productivity periods. These occurrences are attributed to wind/current supply during warmer Oligocene intervals.

Deep water circulation in the Paleocene Ocean

Abstract We have compiled deep water benthic δ 13 C data from the Paleocene portions of several DSDP and ODP holes and present it using the new timescale of Berggren et al. (1995). Our data show that the north Atlantic hole DSDP 384 was the most positive site for δ 13 C in the late Cretaceous and the earliest Paleocene, suggesting that the sub-tropical north Atlantic was an important locus of deep water production during these intervals. Salinity and temperature comparisons do not support unequivocal deep water production by halothermal means in this region so we prefer to avoid the term Warm Saline Deep Water (WSDW) and employ instead the more neutral term ‘palaeo-North Atlantic Deep Water’ (palaeo-NADW). During K/T boundary time, the southern ocean apparently became the major producer of deep waters. Based on δ 13 C comparisons both the North Atlantic and Southern Ocean were deep water producers during the early Paleocene to the late Paleocene interval. In the latest Paleocene (during the ‘Paleocene carbon isotope maximum’) Southern Ocean δ 13 C was most positive, supporting a Southern Ocean deep water source. The earliest Eocene ocean was characterized by deep water production in the high southern latitudes with well developed interbasinal δ 13 C gradients. δ 18 O data show an overall decrease from the late Cretaceous into the Early Eocene interrupted by an increase between 64 and 57 Ma. This is interpreted as an overall warming trend with a superimposed, previously undocumented, cooling phase in the early to late Paleocene.

Multiple deep-water sources and trophic regimes in the latest Cretaceous deep sea: evidence from benthic foraminifera

Benthic foraminifera from 24 DSDP/ODP sites were investigated to assess their global horizontal and vertical distribution in the deep-sea environment at the end of the Cretaceous period. The samples analyzed are from the late Maastrichtian and within the planktic forammiferal Abathomphalus mayaroensis Zone from a wide range of oceans and paleolatitudes, including the low-latitude Sites 10 and 384 (Atlantic Ocean), 47, 171, 305, and 465 (Pacific Ocean), the mid-latitude Sites 20, 111, 356, 363, 516, 525, 527, 548, and 605 (Atlantic Ocean), 216, 217, and 758 (Indian Ocean), and the high-latitude Sites 208 (Pacific Ocean), 689, 698, 700, 738 and 750 (Southern Ocean).Correspondence analysis, based on the 75 most common taxa, shows a clear biogeographic trend along the first correspondence axis by arranging the sites in paleolatitudinal order. The assemblages from the Tethyan Realm (i.e., low latitudes) are marked by abundant heavily calcified buliminids (such as Bulimina incisa B. trinitatensis B. velascoensis, and Reussella szajnochae) and Aragonia spp., whereas high-latitude faunas are characterized by abundant Alabamina creta, Gyroidinoides quadratus, and Pullenia coryelli.The results indicate that the faunas at low and high latitudes, respectively, were influenced by quite different environmental conditions. This is based on the much higher abundance of infaunal morphotypes at low and mid latitudes compared to high latitudes, suggesting that the biogeographic trend found in the data set coincides with the trophic regime at the various sites. The results also provide support for the hypothesis that postulates two simultaneous sources and mechanisms for deep-water formation during the Late Cretaceous, including warm, saline deep water produced by evaporation at low (equatorial) latitudes in contrast to the formation of cold deep waters at high (southern) latitudes.

Middle Miocene deepwater paleoceanography in the southwest Pacific: Relations with East Antarctic Ice Sheet development

A suite of middle Miocene Deep Sea Drilling Project sites in the southwest Pacific reveals large‐scale changes in deepwater circulation associated with East Antarctic Ice Sheet (EAIS) variations from ∼16.5 to 13.8 Ma. Oxygen and carbon isotopic records based on Cibicidoides benthic foraminifera from a depth transect (sites 590B, 588A, 591B, and 206 from 1200‐ to 3150‐m paleodepth at ∼35°S paleolatitude) and from a meridional transect (sites 588A, 590B, 593, and 594 from 30° to 48°S paleolatitude at intermediate water depth) allow detailed examination of southwest Pacific deepwater circulation from ∼17.5 to 12 Ma. Significantly, intervals of low δ18O from 16.5 to 16.3 Ma and perhaps at 15.7 Ma were marked by similar δ18O values at upper bathyal (∼1200–1500 m; sites 588A and 590B) and midbathyal (∼2100 m; site 591B) water depths. Small vertical δ18O gradients during δ18O minima may indicate warm saline deep water (WSDW) at midbathyal depths in the southwest Pacific during intervals of inferred global warmth and low global ice volume. Increased vertical δ18O gradients after ∼15.6 Ma and especially after 13.8 Ma indicate increased production of Southern Component Water (SCW) in association with EAIS growth. These data are consistent with the hypothesis (Woodruff and Savin, 1989) that major EAIS growth was fostered by diminished meridional heat transport to the high southern latitudes related to the termination of Tethyan Indian Saline Water (TISW) and an increase in SCW production during the early middle Miocene after ∼15.6 Ma. Further, a maximum vertical carbon isotopic gradient of ∼0.8 ‰ at 13.6 Ma suggests that Southern Component Intermediate Water (SCIW) production and Pacific Deep Water (PDW) strength were each at a maximum at this time and were critical to major EAIS growth. The establishment of near‐modern δ13C and δ18O gradients following major EAIS growth from ∼14.0 to 13.8 Ma marks a major step in the development of the Neogene ocean/cryosphere system.

Late quaternary paleoceanography of the Banda Sea

A stable oxygen and carbon isotopic record of benthic ( Uvigerina and Cibicidoides species) and planktonic ( Globigerinoides ruber) foraminifera recovered from a deep-sea core in the Banda Sea was obtained to develop a better understanding of surface- and deep water hydrography in this region over the last ~180 kyr. Higher glacial to interglacial δ 18O amplitudes of planktonic and benthic foraminifera (1.8 and 1.7%., respectively) indicate an increase in Banda surface and deep water salinity during glacial conditions. Planktonic data is influenced by the precession (23 kyr periodicity) while benthic values reflect intermediate Pacific water fluctuations. The benthic δ 13C exhibits a depletion of about 0.3%. for the last glacial maximum (LGM) relative to the Holocene. A still higher depletion of benthic δ 13C (0.4–0.6%.) occurs during the penultimate full glaciation (stage 6). The main characteristics of δ 13C in the Banda Sea are a direct record of the δ 13C global oceanic signal and an evolution similar to intermediate and deep Pacific waters. Banda Sea records indicate a general good ventilation that remained unchanged between glacial and interglacial periods. Variations in the carbon isotopic composition of planktonic foraminifera are attributed to the local variability in monsoonal upwelling or changes in throughflow of Pacific intermediate-water masses via Indonesian seas. An increase in the alkalinity and deepening of the lysocline has resulted in higher carbonate content during glacial periods, similar to the results reported in the North Pacific.

Middle Eocene to early Oligocene paleoceanography of the Antarctic Ocean (Maud Rise, ODP Leg 113, Site 689): change from a low to a high productivity ocean

The sediment record from the middle Eocene (about 45 Ma) to the early Oligocene (about 33 Ma) on Maud Rise Site 689, Weddell Sea (paleodepth 1400–1650 m), has been studied by means of a coarse fraction analysis in order to reconstruct variations in surface water productivity and bottom water masses. Productivity has been estimated using carbonate dissolution and accumulation rates of radiolaria, diatoms, benthonic and planktonic foraminifers, sponge debris, ostracods and echinoids. Accumulation rates of Bolboforma spp. vary parallel to these proxies. Productivity increased with time. Three episodes were found in which productivity increased sharply, and productivity varied cyclically with a period of 430 ky. The middle Eocene, ca. 45.44-37.26 Ma, was a period of generally low productivity. No opal was deposited and carbonate preservation was excellent. During periods of a slight increase in productivity accumulation rates of benthonic and planktonic foraminifers, ostracods and echinoids increased in spite of an increase in carbonate dissolution. In the period ca. 41.62–43.07 Ma productivity rose in three distinct pulses. Clinoptilolite, formed from biogenous opal, is a common mineral in these sediments. These three productivity maxima coincide with a mica-rich unit. Mica probably originated from erosion on Antarctica, and was transported by an intermediate water depth current. In the late Eocene, ca. 36.9–34.95 Ma, productivity increased considerably and opal skeletons were deposited. Carbonate dissolution increased but planktonic foraminifer accumulation rates were not markedly decreased in periods of higher productivity, because productivity increase exceeded or equalled rises in dissolution rates. Increasing opal accumulation rates coincided with increases in the rates for benthonic foraminifers, sponge debris, ostracods and echinoids. In the late Eocene-early Oligocene period, 34.95-33.05 Ma, a further increase in productivity led to a strong dissolution of planktonic foraminifers in high productivity periods. The productivity increase is probably due to the increasing pole-equator temperature gradient which led to stronger atmospheric and oceanic turnover and mixing in the oceans. In the uppermost late Eocene two unusual layers suggest changes in bottom water masses affecting the seafloor at Site 689. A sediment interval with especially well-preserved carbonate microfossils underlies an interval that has poor carbonate preservation despite evidence of low productivity. These intervals suggest a change in bottom water conditions from Warm Saline Deep Water (WSDW), which favors carbonate preservation, to Antarctic Bottom water (AABW), which promotes carbonate dissolution. Cooling of surface waters over a period of 300 ky led to a thickening of the deep AABW layer, and an upward shift of the overlying WSDW, until the AABW finally reached the top of the Maud Rise in the area of Site 689. This period of AABW influence on top of the Maud Rise lasted 200 ky.

Review and new aspects concerning the formation of eastern Mediterranean sapropels

In this paper, it is proposed that the formation of eastern Mediterranean sapropels occurred in an anti-estuarine type of circulation, which was to some degree weakened relative to the present in response to reduction of the eastern Mediterranean excess of evaporation over freshwater input. This reduction of excess evaporation would have been imposed by intensifications of (1) the Indian Ocean summer (SW) monsoon, influencing the eastern Mediterranean via increased Nile discharge, and (2) the system of Mediterranean depressions (an element of the westerly Atlantic system) causing increased precipitation and decreased evaporation. Both the Indian Ocean summer monsoon, and the westerly Atlantic system, would be intensified in response to the occurrence of distinct minima in the cycle of precession.It is demonstrated that reduced excess evaporation, whether or not coinciding with global phases of deglaciation, would lead to reduction of surface water salinities in the eastern Mediterranean, causing “isolation” of previously formed high salinity (cooler) deep water. Thus, mixing was severely reduced, possibly even restricted to eddy diffusion, with only occasional convective events that, because of the existing density gradient, hardly ever would reach the deepest parts of the basin. The consequently diminished oxygen advection down from a few hundred meters in the water column, favoured preservation of the sinking organic matter. This would, however, suffice only to enable the formation of sapropels with low organic carbon contents. The high organic carbon contents observed in various sapropels are argued to reflect superimposed increases of export production.The described scenario accounts for previously reported (1) increases of organic carbon content with increasing depth of deposition within individual sapropels, and (2) asymmetrical sequences of sapropel deposition, characterized by gradual build-up and rather abrupt ending. It is, furthermore, in agreement with (3) isotopic and faunal reconstructions of the history of exchange transports through both the Strait of Sicily, and the Strait of Gibraltar, and (4) faunal and floral reflections of the presence or absence of a distinct Deep Chlorophyll Maximum with its associated increases in export production, indicating the presence or absence of a shallow pycnocline within the euphotic layer. Moreover, the described scenario (5) is in no way conflicting with the reports of sapropels in the western Mediterranean, and (6) seems to be endorsed by occasionally intercalated intervals suggestive of somewhat improved oxygenation, amidst anoxic (benthic desert) levels, a situation that has been observed in a few Quaternary and Pliocene sapropels.

The treatment of inconsistencies in Atlantic deep water salinity data

Salinity biases between hydrographic cruises are known to have occurred, and it has been recommended that the uniform characteristics of the basins east of the Mid-Atlantic ridge be used to discern measurement differences between cruises to the region. That approach was used with two high quality north-south eastern Atlantic expeditions (Oceanus Cruise 202[“McTT”] and South Atlantic Ventilation Experiment [“SAVE”] Leg III), to construct a reference to assess the salinity differences between IGY cruises from the 1950s and some more recent expeditions compared to that reference. Tables of salinity differences were prepared so that one may make adjustments to data sets when mapping any characteristic that is sensitive to relative salinity errors, such as computed geostrophic currents, or when mapping any characteristic on density surfaces.

3He and methane in Sakurajima Caldera, Kagoshima Bay, Japan

Volcanic gases from the submerged caldera of Sakurajima Volcano are characterized by 3 He 4 He = 6.1R A , CH 4 3 He ≈ 10 9 , and a ratio of excess ΣCO 2 to 3He of 140 × 10 9. Helium in the Kagoshima Bay waters is a mixture of volcanic helium and atmospheric-solubility helium in surface waters, and provides a strong signature for seawater injected into the protocaldera by flow through the volcanic edifice, the probable source of the warm deep water that replaces the colder, more saline deep water of the North Basin in November.

The middle Miocene climatic transition: East Antarctic ice sheet development, deep ocean circulation and global carbon cycling

The middle Miocene represents a major change in state in Cenozoic climatic evolution, following the climax of Neogene warmth in the late early Miocene at ∼16 Ma. The early stage of this climatic transition from ∼16 to 14.8 Ma was marked by major short term variations in global climates, East Antarctic Ice Sheet (EAIS) volume, sea level, and deep ocean circulation. In the later stage from ∼14.8 to 12.9 Ma, climatic developments included major growth of the EAIS and associated Antarctic cooling, a distinct increase in the meridional temperature gradient, large fluctuations in sea level followed by a global sea level fall, and important changes in deep water circulation, including increased production of Southern Component Water. East Antarctic ice sheet growth and polar cooling also had large effects on global carbon cycling and on the terrestrial biosphere, including aridification of mid-latitude continental regions. Increased stability of the EAIS after 14.8 Ma represents a crucial step in the establishment of late Neogene global climate systems. What controlled these changes in polar climates and the East Antarctic ice sheet? Deep ocean circulation changes probably played a major role in the evolution and variation in polar climates, as they have throughout the Cenozoic. Oxygen and carbon isotopic evidence for warm, saline deep water production in the eastern Tethyan/northern Indian Ocean indicates that meridional heat transport to the Antarctic inhibited Cenozoic polar cooling and EAIS growth during the early middle Miocene from ∼16 to ∼14.8 Ma. Inferred competition between warm low-latitude sources (derived from the eastern Tethyan-northern Indian Ocean) and a cold high-latitude source (Southern Component Water) from ∼16 to 14.8 Ma may have been associated with instability in the Antarctic climate and cryosphere. Reduction of warm, saline deep water flow to the Southern Ocean at ∼14.8 Ma may have decreased meridional heat transport to the Antarctic, cooling the region and leading to increased production of Southern Component Water. These middle Miocene climatic and cryospheric changes in the Antarctic had profound effects on marine and terrestrial climates. As the meridional surface temperature gradient increased, boundaries between climatic zones strengthened, leading to increased aridification of mid-latitude continental regions in Australia, Africa and North and South America, enhancing the development of grasslands and stimulating the evolution of grazing mammals.

Regional Flow in the Baltic Shield During Holocene Coastal Regression

AbstractThe occurrence of saline waters in the Baltic Shield in Sweden is consistent with ongoing but incomplete Holocene flushing and depends on the geometry and connectivity of conductive structures at both regional and local scales, and on the surface topography. Numerical simulation of regional variable‐density fluid flow during Holocene land‐rise and coastal regression shows that the existence of any old saline water, whether derived from submarine recharge in regions below Sweden's highest postglacial coastline or geochemical processes in the crystalline rock, is an indication either of slow fluid movements through the bedrock over long times, or of long travel distances through fracture systems before arriving at measurement points. During the land‐rise period, regional flow is not affected by the variable density of fluids in the upper few kilometers of the shield, and the topography of the water table is the only driving force. The spatial distribution of meteoric flushing water and pre‐Holocene waters may be complex, with the possibility of relatively fresh water in fracture zones below salty units even at depths of a few kilometers. The domination of the topographic driving force implies that deep saline water is not necessarily stagnant, and significant flow may be expected to occur in well‐connected horizons even at depth. Local topography variation and fracture zone location combine to create a complex flow field in which local topographic driving forces extend to considerable depth in some areas, whereas regional topographic forces predominate in others. Thus, a pattern may be difficult to discern in measurements of the regional salinity distribution, although it is clear that the coastal region is the major zone of discharge for deeper pre‐Holocene fluids. During the land‐rise period, the regional flow field equilibrates with changing climatic conditions and coastal positions, while the distribution of flushing water and older water lags and will perpetually change between successive glaciations. These characteristics have direct implications for the safety of nuclear water repositories located at depth in Baltic Shield rocks.

The Paleocene-Eocene transition in the Antarctic Indian Ocean: Inference from planktic foraminifera

Isotopic depth stratification and relative abundance studies of planktic foraminifera at ODP Site 738 reveal three major faunal turnovers during the latest Paleocene and early Eocene, reflecting the climatic and structural changes in the Antarctic surface ocean. Faunal Event 1 occurred near the Paleocene/Eocene boundary and is characterized by a faunal turnover in deep dwellers, decreased relative abundance in intermediate dwellers and increased relative abundance in surface dwellers. This event marks a temporary elimination of the vertical structure in the surface ocean over a period of more than 63,000 years that is apparently associated with the sudden shutdown of the “Antarctic Intermediate Water” production. The appearance of morozovellids before this event suggests that polar warming is the cause for the shutdown in the production of this water mass. At this time warm saline deep water may have formed at low latitudes. Faunal Event 2 occurred near the AP5a/AP5b Subzonal boundary and is characterized by a faunal turnover in deep dwellers with no apparent change in surface and intermediate dwellers. Increased individual size, wall-thickness and relative abundance in deep dwelling chiloguembelinids suggests the formation of a deep oxygen minima in the Antarctic Oceans during the maximum polar warming possibly as a result of upwelling of nutrient-rich deep water. Faunal Event 3 occurred in Subzone AP6 and is characterized by a faunal turnover in surface dwellers and a delayed diversification in deep dwellers. This event marks the onset of Antarctic cooling. A drastic decrease in the δ 13C/δ 18O values of the deep assemblage in Zone AP7 suggests an intensified thermocline and reduced upwelling following the polar cooling.

Exchange of Water and Nutrients Between the Skagerrak and the Kattegat

Simultaneous CTD and current measurements have been made repeatedly at several stations in a cross-section between the Danish island Læsø and the Swedish west coast. The cross-section is situated in the northern Kattegat which forms the outer part of the Baltic estuary. Parallel nutrient and oxygen measurements were made in order to obtain a suitable set of background data for ecological modelling of the Kattegat. Here, this dataset is used to calculate fluxes of water, nutrients and oxygen, as functions of salinity. A division is made between the biologically passive winter period, November to February (when the inorganic nutrients components are nearly conservative) and a biologically active 'summer' period from March to October. A striking feature is the much stronger inflow of high salinity deep water during winter, approximately 64 000 m 3 s -1, compared to only 28 000 m 3 s -1 during summer. The inflow is concentrated to salinities higher than 33 PSU. The surface water outflow occurs in the interval 23 to 27 PSU. While the inflow of oceanic deep water to the Kattegat occurs on the deeper eastern side of Læsø, the outflow of surface water from the Baltic seems to be dominated by the flux west of Læsø.