High-latitude Waters Research Articles

A soil‐vegetation‐atmosphere transfer scheme for the modeling of water and energy balance processes in high latitudes: 2. Application and validation

In support of the overall scientific objective of the Boreal Ecosystem‐Atmosphere Study (BOREAS), which encompasses the improved understanding of the interactions between the boreal forest and the atmosphere, a process‐based water and energy balance model is applied to observed forcing data, and the results are presented and discussed. Observed tower forcing and validation data are analyzed. A consistent diurnal pattern in the energy balance closure of the validation data is obtained. Simulations are performed for a number of BOREAS flux tower sites. The model successfully simulates the temporally averaged Bowen ratio and the evaporative part of precipitation over the different BOREAS flux tower sites during the 1994 and 1996 intensive field campaigns. At finer temporal scales a small phase shift in sensible heat flux and net radiation exists between the observed and model‐derived quantities. The ground heat flux is found to be slightly larger than the observations during the course of the day. It is suggested that the sensitivity of the model to parameters such as the moss thickness, thermal conductivity, and heat capacity is responsible for these differences. The moss moisture content and the different components of the energy balance were very well matched for a continuous simulation during 1996. Overall, the accuracy performance of the model is equivalent to the accuracy of the input forcing data.

A soil‐vegetation‐atmosphere transfer scheme for the modeling of water and energy balance processes in high latitudes: 1. Model improvements

This paper describes the development of a process‐based water and energy balance model for use in high latitudes under both summertime and wintertime conditions. The model is developed as a part of the Boreal Ecosystem‐Atmosphere Study (BOREAS). The model differs from its original version in the representation of hydrological processes specific to climatic and ecologic conditions in high latitudes: the impact of an organic layer on the water and energy balance of the boreal forest; the parameterization of frozen ground and snow accumulation and ablation; and the effect of open water bodies on the calculation of the radiative energy and water budget. The model can be run either in a fully distributed or an aggregated statistical mode. The resulting macroscale hydrological model can be used, off line, to study the energy and water balance of the boreal forest and potentially can be used as a land‐atmosphere parameterization in atmospheric models.

THE LATE PALEOCENE THERMAL MAXIMUM: ANCIENT GLOBAL WARMING AT MODERN RATES?

One of the most abrupt and dramatic ancient global warming events took place ∼55 Ma in the late Paleocene epoch. This event, known as the Late Paleocene Thermal Maximum (LPTM), involved warming of high latitude and subtropical oceanic surface waters by up to 6°C and deep waters by up to 8°C. Deep-water warming and consequent oxygen deficiency led to the most severe mass extinction of deep-sea faunas in the last 90 million years. By contrast, the LPTM is also associated with major speciation of planktic foraminifers and terrestrial mammals. The event corresponds to a large (3 per mil), negative carbon isotope excursion (CIE) that suggests major changes in the nature of carbon cycling. The CIE has been used to correlate the LPTM between terrestrial and marine sediments. Current estimates of the duration of the LPTM range between 50–200 thousands of years. The onset of the event, including the full magnitude of the CIE, is thought to span 2–10 thousands of years. This initial rate of CO2 input is comparable with anthropogenic input of fossil fuels. Possible sources of CO2 and warming mechanisms include dissociation of methane hydrates along continental margins and a major episode of effusive volcanism in the North Atlantic. For causal mechanisms to be fully tested, however, more precise estimates of the duration of the onset are required. In this talk, a state-of-the-art chronology of the LPTM was presented along with a comparison of LPTM and modern CO2 input and warming rates.

Influence of m-cresol purple indicator additions on the pH of seawater samples: correction factors evaluated from a chemical speciation model

Abstract The perturbation of the indicator m -cresol purple on the pH in seawater is illustrated in diagrams, representing measurements in 1-cm and 5-cm cells. The diagrams apply to a measured pH interval of 7.4–8.4 using a 2-mM stock solution of m -cresol purple sodium salt dissolved in seawater. The magnitude of the perturbation is described as correction values, i.e., the change in seawater pH caused by the indicator. The diagrams are based on calculations made by using the equilibrium speciation programme, MARINHALT. From these calculations, and least squares fitting methods, pH correction values are described in terms of the pH difference between each seawater sample and the pH of an indicator stock solution. Calculations are performed for a typical high latitude water and a north Pacific deep water. Diagrams are presented for a salinity of 35 and a temperature of 15°C. Responses to salinities between 32 and 36 and temperatures 15–25°C are illustrated as well. A ±0.05 pH difference between a seawater sample and an indicator stock solution gives a correction of less than 0.001 pH unit for a 1-cm cell. For a 5-cm cell, pH differences between the indicator stock solution and a seawater sample as large as ±0.3 cause corrections smaller than ±0.001 pH unit. Calculations demonstrate that the five-fold lower indicator concentration used with 5-cm cells decreases the perturbation effect by approximately a factor of five relative to 1-cm cells.

Grounding Pleistocene icebergs shape recent deep-water coral reefs

The widespread view that scleractinian corals in cold and deep waters of high latitudes are slow growing organisms that do not form reefs is challenged by the discovery of a huge coral reef over 13 km in length, 10 to 35 m in height and up to 300 m in width formed by the coral Lophelia pertusa in water depths of 270 to 310 m at 64°N on the Sula Ridge, Mid-Norwegian Shelf. Cruises in 1994, 1995 and manned submersible operations in May 1997 provide data and observations from which the structure and development of the Sula Ridge coral reef have been determined. The Fennoscandian icesheet retreated from the Mid-Norwegian shelf prior to 12,000 years before present and modern oceanographic conditions were established at 8000 years before present. Coral growth since that time has resulted in a large deep-water shelf reef for which recent stable isotopic studies have demonstrated high growth rates for these azooxanthellate cold-water corals. Information on the geometry of deep-water coral reefs and their environmental controls is still fragmentary, controversial and raises issues of conservation in this area of active fishing and oil exploration. This paper reports on the discovery of what is probably one of the largest deep-water coral reefs existing in the northeast Atlantic and indicates that its siting is due to post-glacial structures (iceberg plough marks), events (the second Storegga Slide) and local conditions on the seafloor. Surprisingly, reef accumulation rates on the Sula Ridge are comparable with those measured on tropical coral reefs.

Spatial and Temporal Structure of Atmospheric Water Vapor Transport in the Mackenzie River Basin

Abstract The transport of water vapor through the Mackenzie River basin, a typical high-latitude river basin, is examined for the period from August to October 1994. The spatial and temporal variability in the transport is considered with both objectively analyzed fields and radiosonde data. Previous studies of the high-latitude water vapor have made use of radiosonde data and have been able to document some features of annual cycle of water vapor transport. These studies have left unresolved many important aspects of moisture transport processes. In particular, detailed information as to the spatial and temporal variation of the transport has not been fully documented or understood. In order to address these important issues, the authors make use of the objectively analyzed fields from the European Centre for Medium-Range Weather Forecasts to study the high-latitude transport of water vapor. This paper presents findings regarding the transport of water vapor over northern parts of North America. It is sh...

On the structure and the transport of the eastern Weddell Gyre

The circulation pattern and volume transports in the eastern Weddell Gyre are estimated on the basis of hydrographic data collected by R.V. Polarstern between 1989 and 1996. In the northeastern edge of the Weddell Gyre, eastward-flowing water masses from the Antarctic Circumpolar Current and the Weddell Sea converge. Due to the strong effect of topographic constraints on ocean currents in the weakly stratified waters of high latitudes, the wedge-like structure of the Southwest Indian Ridge can cause the convergence. The increased shear leads to instabilities of the current at the eastern end of the ridge, which produce an intense mesoscale eddy field between 15° and 30°E. In the eddies, water from the Weddell cold regime and the Antarctic Circumpolar Current waters mix and form the water masses of the Weddell warm regime. These waters are advected southward and flow towards the westward southern rim current, which is driven by the Antarctic eastwind band. Hence, there is not a continous flow from the northern to the southern rim, but a decay of the mean flow in the northeast and a reformation in the south. Volume transports across the Greenwich Meridian, estimated on the basis of a combined CTD/ADCP data set, result in an eastward flow of 61 Sv in the northern rim current and a westward return flow of 66 Sv in the southern part of the gyre. The transport is about twice as high as previous estimates between Kapp Norvegia and the northern tip of the Antarctic Pensinsula, indicating a significant gyre circulation north of 70°S.

Southern High-Latitude Ocean Climate Drift in a Coupled Model

Abstract Climate drift in coupled models affects the response of the coupled system to an external forcing. In most existing coupled models that employ flux adjustments, the southern high latitudes, in particular, are still affected by some climate drift. In the CSIRO coupled model, within 100 years following coupling, the Antarctic Circumpolar Current (ACC) intensifies by about 30 Sv (Sv ≡ 106 m3 s−1). This happens despite the use of flux adjustments. Many other model fields such as sea ice, surface albedo, and heat fluxes of the coupled system also experience drift from the precoupled spinup states. It is therefore important to study the processes that give rise to these drifts. The primary cause of drift in the CSIRO model is due to changes in the pattern of convection in the Southern Ocean relative to the spinup steady state. Upon coupling, the pattern of convection alters systematically regardless of surface boundary conditions. Consequently, overturning at shallow to intermediate depths (from the surface to about 2000 m) weakens, while that below these depths intensifies. The decline of overturning at shallow to intermediate depths leads to reduced surface temperatures because a lesser amount of warm subsurface water is mixed up into the colder surface mixed layer. The cooler surface temperature leads to an initial increase in sea ice, which is exacerbated by a significant albedo–temperature–sea ice feedback. The resulting increase in sea ice formation at the higher southern latitudes leads to increased brine rejection and a general increase in salinity throughout much of the high-latitude water column. This increase in salinity intensifies deep convection and bottom water formation, driving a stronger ACC. Several additional experiments are performed to trace various oceanic and ocean–atmosphere feedbacks that give the drift its character. It is demonstrated that the feedbacks significant to the drift in the present model are the positive albedo–temperature–sea ice feedback and a negative feedback between sea ice and overturning. The role of these two feedbacks in the interconnection between the drifts in various model fields is discussed.

Southern High-Latitude Ocean Climate Drift in a Coupled Model

Climate drift in coupled models affects the response of the coupled system to an external forcing. In most existing coupled models that employ flux adjustments, the southern high latitudes, in particular, are still affected by some climate drift. In the CSIRO coupled model, within 100 years following coupling, the Antarctic Circumpolar Current (ACC) intensifies by about 30 Sv (Sv ≡ 106 m3 s−1). This happens despite the use of flux adjustments. Many other model fields such as sea ice, surface albedo, and heat fluxes of the coupled system also experience drift from the precoupled spinup states. It is therefore important to study the processes that give rise to these drifts. The primary cause of drift in the CSIRO model is due to changes in the pattern of convection in the Southern Ocean relative to the spinup steady state. Upon coupling, the pattern of convection alters systematically regardless of surface boundary conditions. Consequently, overturning at shallow to intermediate depths (from the surface to about 2000 m) weakens, while that below these depths intensifies. The decline of overturning at shallow to intermediate depths leads to reduced surface temperatures because a lesser amount of warm subsurface water is mixed up into the colder surface mixed layer. The cooler surface temperature leads to an initial increase in sea ice, which is exacerbated by a significant albedo–temperature–sea ice feedback. The resulting increase in sea ice formation at the higher southern latitudes leads to increased brine rejection and a general increase in salinity throughout much of the high-latitude water column. This increase in salinity intensifies deep convection and bottom water formation, driving a stronger ACC. Several additional experiments are performed to trace various oceanic and ocean–atmosphere feedbacks that give the drift its character. It is demonstrated that the feedbacks significant to the drift in the present model are the positive albedo–temperature–sea ice feedback and a negative feedback between sea ice and overturning. The role of these two feedbacks in the interconnection between the drifts in various model fields is discussed.

Zonal extent of oceans, high-latitude fresh water supplies and the thermohaline circulation

Zonal extent of oceans, high-latitude fresh water supplies and the thermohaline circulation

Low-latitude Plio-Pleistocene temporal abundance variations in the radiolarian Cycladophora davisiana Ehrenberg: stratigraphic and palaeoceanographic significance

Abstract The abundance variation of the radiolarian Cycladophora davisiana was recorded throughout the Plio-Pleistocene Olduvai Time-slab of Ocean Drilling Program (ODP) Sites 677, 709, 847, 850 and 851, in the equatorial Pacific and Indian Oceans. Data were plotted on independently erected timescales. Twelve peak-abundance events were recognized, although not all events were recognized at all the sites. Most of the events, where they are recorded at different sites, were synchronous. However, events recorded at Site 709 in the Indian Ocean were found to be approximately 15 ka older than those events recorded at Pacific sites. This age difference may be due to either diachronous C. davisiana events or a slight inaccuracy in the erected timescale for ODP Site 709 compared with those of the eastern Pacific. The previously demonstrated synchroneity of C. davisiana events in the Late Quaternary leads us to believe that the ODP Site 709 timescale may be inaccurate. Thus, recognition of correlatable C. davisiana events in the equatorial Pacific and Indian Oceans permits the further evaluation and fine-tuning of high-resolution timescales, enabling accurate comparisons to be made of sediment sequences on a regional, and possibly oceanic and interoceanic scale. Of the 12 C. davisiana events recognized, only one event occurred at all the investigated sites. This event occurred at c. 1.8 Ma and immediately above the internationally defined Pliocene-Pleistocene boundary, and may thus prove to be a new useful biostratigraphic marker for the Tertiary/Quaternary boundary. C. davisiana is primarily characteristic of high-latitude water masses, therefore the cyclical abundance peaks of this species noted at the low-latitude sites investigated here, represent the injection of deep cold water of high-latitude origin.

The Effect of Cold Climate upon North Atlantic Deep Water Formation in a Simple Ocean–Atmosphere Model

Abstract The sensitivity of North Atlantic Deep Water formation to variations in mean surface temperature is explored with a meridional-vertical plane ocean model coupled to an energy balance atmosphere. It is found that North Atlantic Deep Water formation is favored by a warm climate, while cold climates are more likely to produce Southern Ocean deep water or deep-decoupling oscillations (when the Southern sinking region is halocline covered). This behavior is traced to a cooling-induced convective instability near the North Atlantic sinking region, that is, to unstable horizontal spreading of a halocline that stratifies part of the region. Under the convective instability it is found that climate cooling is generally equivalent to increased freshwater forcing. This is because in a cold climate, high-latitude water masses approach the temperature of maximum density and the convection-driving, upward thermal buoyancy flux induced by surface cooling becomes insufficient to overcome the stratifying effect o...

Burial Diagenesis and Pore-fluid Evolution in a Mesozoic Back-Arc Basin: The Marambio Group, Vega Island, Antarctica

Upper Cretaceous shallow-marine sediments from Vega Island, Antarctica, contain five major authigenic phases; glauconite, pyrite, a zeolite mineral of the clinoptilolite-heulandite group, chlorite, and calcite. The framework sediment composition changes from quartzose at the base of the measured succession to volcaniclastic at the top. The petrogenesis of individual samples reflects the local controls on diagenesis of depositional environment and sediment composition, combined with the effects of burial to no more than 1 km. Calcite cements are the most abundant precipitates. Marine carbonate cements include acicular and other fringing cements that commonly are present within bioclasts. Early-burial micritic to sparry calcite cements include both concretionary and nonconcretionary forms. Burial calcites occlude residual porosity, replace detrital grains and form veins with fibrous and cone-in-cone textures. The stable-isotope composition of the carbonate cements is very variable, with delta 18 O ranging from 0.60 per thousand to - 19.93 per thousand PDB and delta 13 C of - 1.33 per thousand to - 28.09 per thousand PDB. The stable-isotope data reflect the initial conditions of mineral precipitation in oxic and anoxic marine pore waters, together with the effects of subsequent fluid/rock interaction through both recrystallization and cementation. The latest precipitates, thought to have been formed during over pressuring, define a vertical field for burial calcite on an isotope cross plot, suggesting that late fluids responsible for cementation and alteration of earlier precipitates had negative delta 18 O and contained carbon with variable delta 13 C. The oxygen values are compatible with either influx of high-latitude meteoric water or intense fluid-rock interaction with reactive volcanic detritus, or a combination of the two processes. The very variable carbon signatures probably reflect dissolution of bioclasts and earlier diagenetic precipitates. Only by identifying possible end-member compositions for both early and late diagenetic precipitates can most of the isotopic data be interpreted correctly.

Paleoclimate, controls on Upper Devonian source rock sequences and stacked extinctions

High quality (>2% TOC) Upper Devonian source rocks are developed in several sequence types. The commonest type, accounting for 70% of the studied examples is the transgressive sequence with a basal hiatus. Others include shallowing upward sequences (12%), lacustrine sequences in fault-controlled basins (7%), distal slope sequences (7%), and evaporite capped sequences (4%).Starting from the synthesis of Johnson, Klapper, and Sandberg (1985) it has been possible to demonstrate correlativity of Upper Devonian transgressive episodes globally. The marked association of epeiric sea Upper Devonian source rocks with transgressions heightens interest in their causation. Could they have been produced by glacio-eustatic sea-level change as Stanley (1984; 1988) implies? Quantitative paleoclimate modeling and isotopic paleotemperatures for the Upper Devonian suggest not. Modeling using CCM1 at NCAR, including five year seasonal cycles, suggests the absence of any large southern hemisphere ice volume. Because much of the Upper Devonian land mass was either in equatorial or high latitude regions, there was little development of monsoonal climates. Midlatitude cyclonic activity was also much less than at present, meaning less polar transport of moisture and drier polar areas. Precipitation maxima largely coincided with topographic elevations. In contrast to the Late Ordovician to earliest Silurian, there was no Upper Devonian perennial snow cover even over the high latitude southern land mass. This was in spite of winter land temperatures as low as -40°. in eastern Gondwana. In that area and elsewhere, there was thin winter snow cover which melted in late spring resulting in no build-up of snow cover to produce glaciation. This was mainly the consequence of low winter precipitation in Gondwana. High latitude sea surface temperatures were certainly cold enough to displace or exclude some organisms. However, in low latitude areas where Upper Devonian extinctions also took place, modeled sea surface temperatures range between 27° and 34°. Such areas would have been refuges for any organisms displaced by cold, high latitude waters. The higher temperature values of low latitudes are convergent with the isotopic paleotemperatures determined by Brand (1989) using well preserved Upper Devonian brachiopods. Brand's determinations suggest temperatures even reaching lethal values for many plankton (37°). The extinction of reefs by the close of Frasnian time could have been partly a result of such elevated temperatures. Stacked extinctions of conodonts (Ziegler and Lane, 1987) and acritarchs may have been a further result. The loss of reefs, an important consumer of plankton, may have permitted a relative increase in plankton abundance crossing from more oceanic areas into epeiric seas, possibly contributing to high quality source rock deposition.

Three-dimensional simulations of the impact of Southern Ocean nutrient depletion on atmospheric CO2 and ocean chemistry

Surface nutrient concentrations in the Southern Ocean are an important indicator of the atmosphere-ocean chemical balance that played a key role in ice-age reduction of atmospheric pC0, and would play a role in any Fe fertilization scenario for increasing oceanic uptake of anthropogenic CO,. The response of the ocean and atmosphere to a scenario of extreme depletion of Southern Ocean surface nutrients by an increase in the organic matter flux to the deep ocean is examined with a three-dimensional model of ocean circulation coupled to a one-box model of the atmosphere. After 100 yr, the increase in the organic matter flux is 6-30 Gt C yr-l-about twice the global new production determined by the same model for the present ocean. The removal of nutrients from surface waters of the Southern Ocean reduces the nutrient content of the near-surface and intermediate depth waters of the entire ocean, resulting in a 0.5-l .9 Gt C yr-’ reduction of low-latitude new production. The deep circumpolar waters, enriched in nutrients by regeneration of organic matter, spread into the deep and bottom waters of the remainder of the ocean, giving an overall downward shift of nutrients from surface and intermediate to circumpolar and deep waters. The oceanic total C distribution is also shifted downward, resulting in uptake of atmospheric CO, of 46-85 ppm (98-181 Gt C) in the first 100 yr. The oxygen content shifts upward in the water column, approximately mirroring the downward shift of nutrients. Some of the oxygen shifted to the upper ocean escapes to the atmosphere. As a consequence, the global average oceanic content of oxygen, presently 168 pmol kg-l, is reduced by 6-20 pmol kg-l, with anoxia developing in the southwestern Indian Ocean. CO2 is unusual compared to other atmospheric gases because most of the combined atmosphere-ocean inventory (98.5%) is in the ocean. By contrast, oxygen, a more typical atmospheric gas, has only 0.6% of its atmosphere-ocean inventory in the ocean. CO2 is m 30 times as soluble as oxygen, due mainly to hydrogen bonding with water molecules; however, the primary reason for the large amount of CO2 in the ocean is that it reacts with water to form HCO,and Acknowledgments This work was supported by the U.S. Department of Energy under contract DEFG 02-90ER611052, by the National Science Foundation (OCE 9012333), and by GFDWNOAA through the generosity of K. Bryan and J. Mahlman. The perturbation approach for modeling total C was developed in collaboration with U. Siegenthaler. The collaboration of J.L.S. with F. Joos and U. Siegenthaler in earlier high-latitude, nutrient-depletion studies gave us considerable insight into how to go about our threedimensional experiment and how to interpret the results. B. Flannery was the first member of our group to do a nutrient-depletion experiment (summer 1989), following the basic modeling approach developed by R. Najjar. Collaboration of J.C.O. with R. Najjar, R. Slater, and K. Dixon aided in modeling and analysis. COS2-. Only + 1% of the dissolved inorganic C is in the non-ionic CO, form (e.g. Broecker and Peng 1982). Another important contributor to reduced atmospheric CO, levels results from the distribution of total inorganic CO2 (i.e. the sum of the concentrations of C02, and HC03and C032ions), which is IV 12% lower at the surface than at depth. Part of this surface-to-deep difference is due to what is referred to as the “solubility pump” (Volk and Hoffert 1985). CO, is more than twice as soluble in the cold, high-latitude waters which sink to form the deep waters of the ocean, than it is in warm, low-latitude waters (Weiss 1974). However, the primary source of the surface to deep difference is the “biological pump” (Volk and. Hoffert 19 8 5). Photosynthesis produces organic C from CO, in the euphotic zone of the ocean, depleting surface nutrients to near-zero levels over most of the surface ocean. Although most of the photosynthetically produced organic C is recycled in the euphotic zone, -30% either sinks to the deep ocean or is transported there by circulation before being regenerated to CO,.

Simulated circulation of an idealized ocean for Pangaean time

An eight‐level dynamical ocean model, driven by prescribed surface forcing (wind stress, temperature, precipitation‐minus‐evaporation) from a previously published Pangaean time climate simulation, is used to study possible features of ocean circulation, temperature, and salinity for the early Mesozoic. The simulations are sensitivity experiments rather than estimates of the actual circulation because many simplifying assumptions are made concerning the prescribed surface forcing and the ocean basin's shape and depth. Simulated features include relatively warm water in high latitudes, warm deep water, a westward flowing equatorial current across Panthalassa and into the Tethys Sea, poleward and eastward flowing currents along the Tethys coasts, and relatively vigorous meridional and longitudinal vertical overturning cells. Cool, relatively fresh polar water combines with warm, saline Tethys water to produce the relatively warm deep water. There are few geological estimates of early Mesozoic (Pangaean time) ocean circulation available for comparison with the simulated circulation.

A Dynamical Interpretation of the Tritium Maximum in the Central Equatorial Pacific

Abstract The tropical tritium distribution between 1974 and 1981 is characterized by a maximum along the equator centered between 125° and 145°W. It signifies that this region has received the maximum input of high northern latitude water. A dynamical interpretation of the maximum shows that it can be explained by the strength of the Sverdrup circulation in the central equatorial Pacific where there is a strong zonal convergence in the North Equatorial Countercurrent (NECC) and a strong meridional geostrophic flow towards the equator.

Deepwater source variations during the last climatic cycle and their impact on the global deepwater circulation

The degree of similarity of the ∂13C records of the planktonic foraminiferal speciesN. pachydermaand of the benthic foraminiferal genusCibicidesin the high‐latitude basins of the world ocean is used as an indicator of the presence of deepwater sources during the last climatic cycle. Whereas continuous formation of deep water is recognized in the southern ocean, the Norwegian Sea stopped acting as a sink for surface water during isotope stage 4 and the remainder of the last glaciation. However, deep water formed in the north Atlantic south of the Norwegian Sea during the last climatic cycle as early as isotope substage 5d, and this area was also the only active northern source during stages 4–2. A detailed reconstruction of the geographic distribution of ∂13C in benthic foraminifera in the Atlantic Ocean during the last glacial maximum shows that the most important deepwater mass originated from the southern ocean, whereas the Glacial North Atlantic Deep Water cannot be traced south of 40°N. At shallower depth an oxygenated13C rich Intermediate Water mass extended from 45°N to 15°S. In the Pacific Ocean a ventilation higher than the modern one was also found in open ocean in the depth range 700–2600 m and is best explained by stronger formation of Intermediate Water in high northern latitudes.

The Penetration of Tritium into the Tropical Pacific

Abstract The persistence of subsurface tritium maxima coincident with the Equatorial Currents is used to show that advection along isopycnals by the mean wind-driven circulation is the dominant process in the at most 14-year time scale for the penetration of high northern latitude water to the equator (above 26.2 sigma-theta). Ventilation of the equatorial Pacific thermocline from the north contrasts sharply with the equatorial Atlantic thermocline which is ventilated from the south. The most striking manifestation of the North Pacific circulation is evidenced by a tritium maximum and salinity minimum at the equator between 145° and 125°W located above 25.6 sigma-theta. It shows that regardless of time of sampling the eastern&sol/central equator has received the moat high latitude water, probably as a consequence of recirculation by the Equatorial Currents. Between the same meridians there is a tritium maximum on and north of the equator at the surface, which is interpreted as an expression of upwelling. ...

Geochemistry of Early Permian cold-water carbonates (Tasmania, Australia)

The Permian carbonates of Tasmania formed at a paleolatitude near 80°S during the Gondwanan Ice Age, contain abundant erratic fragments and dropstones, and are associated with glacio-marine sediments. A shallow-marine carbonate depositional model with floating icebergs, calved from an adjacent ice shelf grading into an ice sheet, which was recently proposed by the author, has been used. As sea-level rose during warmer periods, large volumes of melt-waters mixed with marine waters, retarding limestone deposition and causing deposition of shales/siltstones. In ignited samples, CaO, SiO 2 and Al 2O 3 account for ⋍90% of major elements with minor amounts of K 2O, Na 2O, MgO and Fe 2O 3. The silt-size terrigenous fraction in most samples have a high SiO 2 content, far in excess of that attributable to clay minerals. The Ga and Rb concentrations indicate a change from normal marine conditions during limestone deposition to brackish and freshwater conditions during shale deposition. Decreasing values of Sr with increasing concentrations of Mn indicate an open flow of waters in a mixed marine environment. Higher Mn and lower Sr values in the shoreward sequences than in the offshore sequence might be due to regional flow of meltwater from shore to offshore regions. The calculated δ 18O SMOW-values (−8 to −21‰) of waters in equilibrium with the Berriedale Limestone carbonates correspond to high-latitude waters, indicating substantial subsurface low-temperature diagenesis involving melt-waters. The Sr/Mn values decrease with increasingly lighter δ 12C-values due to extensive dissolution of CaCO 3.