Biomass of mesozooplankton in the western part of the Black Sea in summer 1991 during the NATO Programme Hydroblack

The "Hydroblack91" dataset is based on samples collected in the summer of 1991 and covers part of North-Western in front of Romanian coast and Western Black Sea (Bulgarian coasts) (between 43°30' - 42°10' N latitude and 28°40'- 31°45' E longitude). Mesozooplankton sampling was undertaken at 20 stations. The whole dataset is composed of 72 samples with data of zooplankton species composition, abundance and biomass. Samples were collected in discrete layers 0-10, 0-20, 0-50, 10-25, 25-50, 50-100 and from bottom up to the surface at depths depending on water column stratification and the thermocline depth. Zooplankton samples were collected with vertical closing Juday net,diameter - 36cm, mesh size 150 µm. Tows were performed from surface down to bottom meters depths in discrete layers. Samples were preserved by a 4% formaldehyde sea water buffered solution. Sampling volume was estimated by multiplying the mouth area with the wire length. Mesozooplankton abundance: The collected materia was analysed using the method of Domov (1959). Samples were brought to volume of 25-30 ml depending upon zooplankton density and mixed intensively until all organisms were distributed randomly in the sample volume. After that 5 ml of sample was taken and poured in the counting chamber which is a rectangle form for taxomomic identification and count. Large (> 1 mm body length) and not abundant species were calculated in whole sample. Counting and measuring of organisms were made in the Dimov chamber under the stereomicroscope to the lowest taxon possible. Taxonomic identification was done at the Institute of Oceanology by Asen Konsulov using the relevant taxonomic literature (Mordukhay-Boltovskoy, F.D. (Ed.). 1968, 1969,1972). The biomass was estimated as wet weight by Petipa, 1959 (based on species specific wet weight). Wet weight values were transformed to dry weight using the equation DW=0.16*WW as suggested by Vinogradov & Shushkina, 1987. Taxon-specific abundance: The collected material was analysed using the method of Domov (1959). Samples were brought to volume of 25-30 ml depending upon zooplankton density and mixed intensively until all organisms were distributed randomly in the sample volume. After that 5 ml of sample was taken and poured in the counting chamber which is a rectangle form for taxomomic identification and count. Copepods and Cladoceras were identified and enumerated; the other mesozooplankters were identified and enumerated at higher taxonomic level (commonly named as mesozooplankton groups). Large (> 1 mm body length) and not abundant species were calculated in whole sample. Counting and measuring of organisms were made in the Dimov chamber under the stereomicroscope to the lowest taxon possible. Taxonomic identification was done at the Institute of Oceanology by Asen Konsulov using the relevant taxonomic literature (Mordukhay-Boltovskoy, F.D. (Ed.). 1968, 1969,1972). The biomass was estimated as wet weight by Petipa, 1959 ussing standard average weight of each species in mg/m3. WW were converted to DW by equation DW=0.16*WW (Vinogradov ME, Sushkina EA, 1987).

Benthic foraminiferal assemblages and paleoproductivity reconstructions for the last 550 kyr of the Ontong Java Plateau, western equatorial Pacific

We analyzed foraminiferal and nannofossil assemblages and stable isotopes in samples from ODP Hole 807A on the Ontong Java Plateau in order to evaluate productivity and carbonate dissolution cycles over the last 550 kyr (kilo year) in the western equatorial Pacific. Our results indicate that productivity was generally higher in glacials than during interglacials, and gradually increased since MIS 13. Carbonate dissolution was weak in deglacial intervals, but often reached a maximum during interglacial to glacial transitions. Carbonate cycles in the western equatorial Pacific were mainly influenced by changes of deep-water properties rather than by local primary productivity. Fluctuations of the estimated thermocline depth were not related to glacial to interglacial alternations, but changed distinctly at ~280 kyr. Before that time the thermocline was relatively shallow and its depth fluctuated at a comparatively high amplitude and low frequency. After 280 kyr, the thermocline was deeper, and its fluctuations were at lower amplitude and higher frequency. These different patterns in productivity and thermocline variability suggest that thermocline dynamics probably were not a controlling factor of biological productivity in the western equatorial Pacific Ocean. In this region, upwelling, the influx of cool, nutrient-rich waters from the eastern equatorial Pacific or of fresh waters from rivers have probably never been important, and their influence on productivity has been negligible over the studied period. Variations in the inferred productivity in general are well correlated with fluctuations in the eolian flux as recorded in the northwestern Pacific, a proxy for the late Quaternary history of the central East Asian dust flux into the Pacific. Therefore, we suggest that the dust flux from the central East Asian continent may have been an important driver of productivity in the western Pacific.

(Table 1) Radiocarbon ages of ODP Hole 146-893A

High-resolution planktonic foraminiferal census data from Santa Barbara Basin (Ocean Drilling Program hole 893A) demonstrate major assemblage switches between 25 and 60 ka that were associated with Dansgaard-Oeschger cycles. Stadials dominated by Neogloboquadrina pachyderma (sinistral), and Globigerinoides glutinata suggest a strong subpolar California Current influence, while interstadials marked by abundant N. pachyderma (dextral) and G. bulloides indicate a relative increase in subtropical countercurrent influence. Modern analog technique and transfer function (F-20RSC) temperature reconstructions support d18O evidence of large rapid (70 years or less) sea surface temperature shifts (3° to 5°C) between stadials and interstadials. Changes in the vertical temperature gradient and water column structure (thermocline depth) are recorded by planktonic faunal oscillations suggest bimodal stability in the organization of North Pacific surface ocean circulation. Santa Barbara Basin surface water demonstrates the rapid response of the California Current System to reorganization of North Pacific atmospheric circulation during rapid climate change.

Stable isotope and Mg/Ca ratio of sediment core GeoB12610-2

To reconstruct the still poorly understood thermocline fluctuations in the western tropical Indian Ocean, a sediment core located off Tanzania (GeoB12610-2; 04°49.00'S, 39°25.42'E, 399?m water depth) covering the last 35 ka was analysed. Mg/Ca-derived temperatures from the planktonic foraminifera Globigerinoides ruber (white) and Neogloboquadrina dutertrei indicate that the last glacial was ~2.5 °C colder in the surface waters and ~3.5 °C colder in the thermocline compared with the present day. The depth of the thermocline and thus the stratification of the water column were shallower during glacial periods and deepened during the deglaciation and Holocene. The increased inflow of Southern Ocean Intermediate Waters via 'ocean tunnels' appears to cool the thermocline from below, leading to a similarity between the thermocline record of GeoB12610-2 with the Antarctic EDML temperature curve during the glacial. With rising sea level and the corresponding greater inflow of Red Sea Waters and Indonesian Intermediate Waters, the proportion of Southern Ocean Intermediate Water within the South Equatorial Current is reduced and, by Holocene time, the correlation to Antarctica is barely traceable. Comparison with the eastern Indian Ocean reveals that the thermocline depth reverses from the last glacial to present.

Derivation of lake mixing and stratification indices from high-resolution lake buoy data

Lake Analyzer is a numerical code coupled with supporting visualization tools for determining indices of mixing and stratification that are critical to the biogeochemical cycles of lakes and reservoirs. Stability indices, including Lake Number, Wedderburn Number, Schmidt Stability, and thermocline depth are calculated according to established literature definitions and returned to the user in a time series format. The program was created for the analysis of high-frequency data collected from instrumented lake buoys, in support of the emerging field of aquatic sensor network science. Available outputs for the Lake Analyzer program are: water temperature (error-checked and/or down-sampled), wind speed (error-checked and/or down-sampled), metalimnion extent (top and bottom), thermocline depth, friction velocity, Lake Number, Wedderburn Number, Schmidt Stability, mode-1 vertical seiche period, and Brunt-Väisälä buoyancy frequency. Secondary outputs for several of these indices delineate the parent thermocline depth (seasonal thermocline) from the shallower secondary or diurnal thermocline. Lake Analyzer provides a program suite and best practices for the comparison of mixing and stratification indices in lakes across gradients of climate, hydro-physiography, and time, and enables a more detailed understanding of the resulting biogeochemical transformations at different spatial and temporal scales.

Surface wind stress modeled for the Panama Seaway with the Community Climate System Model 3

The early Pliocene warm phase was characterized by high sea surface temperatures and a deep thermocline in the eastern equatorial Pacific. A new hypothesis suggests that the progressive closure of the Panamanian seaway contributed substantially to the termination of this zonally symmetric state in the equatorial Pacific. According to this hypothesis, intensification of the Atlantic meridional overturning circulation (AMOC) - induced by the closure of the gateway - was the principal cause of equatorial Pacific thermocline shoaling during the Pliocene. In this study, twelve Panama seaway sensitivity experiments from eight ocean/climate models of different complexity are analyzed to examine the effect of an open gateway on AMOC strength and thermocline depth. All models show an eastward Panamanian net throughflow, leading to a reduction in AMOC strength compared to the corresponding closed-Panama case. In those models that do not include a dynamic atmosphere, deepening of the equatorial Pacific thermocline appears to scale almost linearly with the throughflow-induced reduction in AMOC strength. Models with dynamic atmosphere do not follow this simple relation. There are indications that in four out of five models equatorial wind-stress anomalies amplify the tropical Pacific thermocline deepening. In summary, the models provide strong support for the hypothesized relationship between Panama closure and equatorial Pacific thermocline shoaling.

(Appendix) Stable carbon and oxygen isotopes, and Mg/Ca ratios of foraminifera from ODP Hole 154-925A

To better understand the links between the carbon cycle and changes in past climate over tectonic timescales we need new geochemical proxy records of secular change in silicate weathering rates. A number of proxies are under development, but some of the most promising (e.g. palaeoseawater records of Li and Nd isotope change) can only be employed on such large samples of mono-specific foraminifera that application to the deep sea sediment core archive becomes highly problematic. "Dentoglobigerina" venezuelana presents a potentially attractive target for circumventing this problem because it is a typically large (> 355 ?m diameter), abundant and cosmopolitan planktic foraminifer that ranges from the early Oligocene to early Pliocene. Yet considerable taxonomic and ecological uncertainties associated with this taxon must first be addressed. Here, we assess the taxonomy, palaeoecology, and ontogeny of "D." venezuelana using stable isotope (oxygen and carbon) and Mg/Ca data measured in tests of late Oligocene to early Miocene age from Ocean Drilling Program (ODP) Site 925, on Ceara Rise, in the western equatorial Atlantic. To help constrain the depth habitat of "D." venezuelana relative to other species we report the stable isotope composition of selected planktic foraminifera species within Globigerina, Globigerinoides, Paragloborotalia and Catapsydrax. We define three morphotypes of "D." venezuelana based on the morphology of the final chamber and aperture architecture. We determine the trace element and stable isotope composition of each morphotype for different size fractions, to test the validity of pooling these morphotypes for the purposes of generating geochemical proxy datasets and to assess any ontogenetic variations in depth habitat. Our data indicate that "D." venezuelana maintains a lower thermocline depth habitat at Ceara Rise between 24 and 21 Ma. Comparing our results to published datasets we conclude that this lower thermocline depth ecology for the Oligo-Miocene is part of an Eocene-to-Pliocene evolution of depth habitat from surface to sub-thermocline for "D." venezuelana. Our size fraction data advocate the absence of photosymbionts in "D." venezuelana and suggest that juveniles calcify higher in the water column, descending into slightly deeper water during the later stages of its life cycle. Our morphotype data show that d18O and d13C variation between morphotypes is no greater than within-morphotype variability. This finding will permit future pooling of morphotypes in the generation of the "sample hungry" palaeoceanographic records.

Sea surface temperature estimation of sediment core 86014-12PC51

A recently developed technique for determining past sea surface temperatures (SST), based on an analysis of the unsaturation ratio of long chain C37 methyl alkenones produced by Prymnesiophyceae phytoplankton (U37 k' ), has been applied to an upper Quaternary sediment core from the equatorial Atlantic. U37 k' temperature estimates were compared to those obtained from delta18O of the planktonic foraminifer Globigerinoides sacculifer and of planktonic foraminiferal assemblages for the last glacial cycle. The alkenone method showed 1.8°C cooling at the last glacial maximum, about 1/2 to 1/3 of the decrease shown by the isotopic method (6.3°C) and foraminiferal modern analogue technique estimates for the warm season (3.8°C). Warm season foraminiferal assemblage estimates based on transfer functions are out of phase with the other estimates, showing a 1.4°C drop at the last glacial maximum with an additional 0.9°C drop in the deglaciation. Increased alkenone abundances, total organic carbon percentage and foraminiferal accumulation rates in the last glaciation indicate an increase in productivity of as much as 4 times over present day. These changes are thought to be due to increased upwelling caused by enhanced winds during the glaciation. If U37 k' estimates are correct, as much as 50-70% (up to 4.5°C) of estimated delta18O and modern analogue temperature changes in the last glaciation may have been due to changes in thermocline depth, whereas transfer functions seem more strongly influenced by seasonality changes. This indicates these estimates may be influenced as strongly by other factors as they are by SST, which in the equatorial Atlantic was only reduced slightly in the last glaciation.

Radiocarbon age, Mg/Ca and d18O measurements on planktonic foraminifera of sediment core GeoB12605-3

The sea surface temperature (SST) of the tropical Indian Ocean is a major component of global climate teleconnections. While the Holocene SST history is documented for regions affected by the Indian and Arabian monsoons, data from the near-equatorial western Indian Ocean are sparse. Reconstructing past zonal and meridional SST gradients requires additional information on past temperatures from the western boundary current region. We present a unique record of Holocene SST and thermocline depth variations in the tropical western Indian Ocean as documented in foraminiferal Mg/Ca ratios and d18O from a sediment core off northern Tanzania. For Mg/Ca and thermocline d18O, most variance is concentrated in the centennial to bicentennial periodicity band. On the millennial time scale, an early to mid-Holocene (~7.8-5.6 ka) warm phase is followed by a temperature drop by up to 2°C, leading to a mid-Holocene cool interval (5.6-4.2 ka). The shift is accompanied by an initial reduction in the difference between surface and thermocline foraminiferal d18O, consistent with the thickening of the mixed layer and suggestions of a strengthened Walker circulation. However, we cannot confirm the expected enhanced zonal SST gradient, as the cooling of similar magnitude had previously been found in SSTs from the upwelling region off Sumatra and in Flores air temperatures. The SST pattern probably reflects the tropical Indian Ocean expression of a large-scale climate anomaly rather than a positive Indian Ocean Dipole-like mean state.

Planktonic foraminiferal flux and shell geochemistry data in the sediment trap time series JAM 1-3 off south Java

Results from sediment trap experiments conducted in the seasonal upwelling area off south Java from November 2000 until July 2003 revealed significant monsoon-, El Niño-Southern Oscillation-, and Indian Ocean Dipole-induced seasonal and interannual variations in flux and shell geochemistry of planktonic foraminifera. Surface net primary production rates together with total and species-specific planktonic foraminiferal flux rates were highest during the SE monsoon-induced coastal upwelling period from July to October, with three species Globigerina bulloides, Neogloboquadrina pachyderma dex., and Globigerinita glutinata contributing to 40% of the total foraminiferal flux. Shell stable oxygen isotopes (d18O) and Mg/Ca data of Globigerinoides ruber sensu stricto (s.s.), G. ruber sensu lato (s.l.), Neogloboquadrina dutertrei, Pulleniatina obliquiloculata, and Globorotalia menardii in the sediment trap time series recorded surface and subsurface conditions. We infer habitats of 0-30 m for G. ruber at the mixed layer depth, 60-80 m (60-90 m) for P. obliquiloculata (N. dutertrei) at the upper thermocline depth, and 90-110 m (100-150 m) for G. menardii in the 355-500 mm (>500 µm) size fraction corresponding to the (lower) thermocline depth in the study area. Shell Mg/Ca ratio of G. ruber (s.l. and s.s.) reveals an exponential relationship with temperature that agrees with published relationships particularly with the Anand et al. (2003) equations. Flux-weighted foraminiferal data in sediment trap are consistent with average values in surface sediment samples off SW Indonesia. This consistency confirms the excellent potential of these proxies for reconstructing past environmental conditions in this part of the ocean realm.

Optimizing PAT data transmission: assessing the accuracy of temperature summary data to estimate environmental conditions

Pop-up archival tags (PAT) provide summary and high-resolution time series data at predefined temporal intervals. The limited battery capabilities of PATs often restrict the transmission success and thus temporal coverage of both data products. While summary data are usually less affected by this problem, as a result of its lower size, it might be less informative. We here investigate the accuracy and feasibility of using temperature at depth summary data provided by PATs to describe encountered oceanographic conditions. Interpolated temperature at depth summary data was found to provide accurate estimates of three major thermal water column structure indicators: thermocline depth, stratification and ocean heat content. Such indicators are useful for the interpretation of the tagged animal's horizontal and vertical behaviour. The accuracy of these indicators was found to be particularly sensitive to the number of data points available in the first 100 m, which in turn depends on the vertical behaviour of the tagged animal. Based on our results, we recommend the use of temperature at depth summary data as opposed to temperature time series data for PAT studies; doing so during the tag programming will help to maximize the amount of transmitted time series data for other key data types such as light levels and depth.

Swimming depth, ambient water temperature preference, and feeding frequency of young Pacific bluefin tuna (Thunnus orientalis) determined with archival tags

We investigated the migration and behavior of young Pacific Bluefin tuna (Thunnus orientalis) using archival tags. The archival tag measures environmental variables, records them in its memory, and estimates daily geographical locations based on measured light levels. Of 166 archival tags implanted in Pacific bluefin tuna that were released at the northeastern end of the East China Sea from 1995 to 1997, 30 tags were recovered, including one from a fish that migrated across the Pacific. This article describes swimming depth, ambient water temperature, and feeding frequency of young Pacific bluefin tuna based on retrieved data. Tag performance, effect of the tag on the fish, and horizontal movements of the species are described in another paper. Young Pacific bluefin tuna swim mainly in the mixed layer, usually near the sea surface, and swim in deeper water in daytime than at nighttime. They also exhibit a pattern of depth changes, corresponding to sunrise and sunset, apparently to avoid a specific low light level. The archival tags recorded temperature changes in viscera that appear to be caused by feeding, and those changes indicate that young Pacific bluefin tuna commonly feed at dawn and in the daytime, but rarely at dusk or at night. Water temperature restricts their distribution, as indicated by changes in their vertical distribution with the seasonal change in depth of the thermocline and by the fact that their horizontal distribution is in most cases confined to water in the temperature range of 14−20°C.

Can the subtropical North Atlantic permanent thermocline be observed from space?

The analysis of remotely sensed altimeter data and in situ measurements shows that ERS 2 radar can monitor the ocean permanent thermocline from space. The remotely sensed sea level anomaly data account for similar to 2/3 of the temperature variance or vertical displacement of isotherms at a depth of similar to 550 m in the Subtropical North Atlantic Ocean near 32.5 degree N. This depth corresponds closely to the region of maximum temperature gradient in the permanent thermocline where near semi-annual internal vertical displacements reach 200 to 300 m. The gradient of the altimeter sea level anomaly data correlates well with measured ocean currents to a depth of 750 m. It is shown that observations from space can account for similar to 3/4 of the variance of ocean currents measured in situ in the permanent thermocline over a 2-y period. The magnification of the permanent thermocline displacement with respect to the displacement of the sea surface was determined as - x650 and gives a measure of the ratio of barotropic to baroclinic decay scale of geostrophic current with depth. The overall results are used to interpret an eight year altimeter data tie series in the Subtropical North Atlantic at 32.5 degree N which shows a dominant wave or eddy period near 200 days, rather than semi-annual and increases in energy propagating westward in 1995 (west of 25 degree W). The effects of rapid North Atlantic Oscillation climate change on ocean circulation are discussed. The altimeter data for the Atlantic were Fourier analysed. It is shown how the annual and semi-annual components relate to the seasonal maximum cholorophyll-a SeaWiFS signal in tropical and equatorial regions due to the lifting of the thermocline caused by seasonally varying ocean currents forced by wind stress.

Characterization of late Campanian and Maastrichtian planktonic foraminiferal depth habitats and vital activities based on stable isotopes

Depth habitats of 56 late Cretaceous planktonic foraminiferal species from cool and warm climate modes were determined based on stable isotope analyses of deep-sea samples from the equatorial Pacific DSDP Sites 577A and 463, and South Atlantic DSDP Site 525A. The following conclusions can be reached: Planoglobulina multicamerata (De Klasz) and Heterohelix rajagopalani (Govindan) occupied the deepest plankton habitats, followed by Abathomphalus mayaroensis (Bolli), Globotruncanella havanensis (Voorwijk), Gublerina cuvillieri Kikoine, and Laeviheterohelix glabrans (Cushman) also at subthermocline depth. Most keeled globotruncanids, and possibly Globigerinelliodes and Racemiguembelina species, lived at or within the thermocline layer. Heterohelix globulosa (Ehrenberg) and Rugoglobigerina, Pseudotextularia and Planoglobulina occupied the subsurface depth of the mixed layer, and Pseudoguembelina species inhabited the surface mixed layer. However, depth ranking of some species varied depending on warm or cool climate modes, and late Campanian or Maastrichtian age. For example, most keeled globotruncanids occupied similar shallow subsurface habitats as Rugoglobigerina during the warm late Campanian, but occupied the deeper thermocline layer during cool climatic intervals. Two distinct types of "vital effect" mechanisms reflecting photosymbiosis and respiration effects can be recognized by the exceptional delta13C signals of some species. (1) Photosymbiosis is implied by the repetitive pattern of relatively enriched delta13C values of Racemiguembelina (strongest), Planoglobulina, Rosita and Rugoglobigerina species, Pseudoguembelina excolata (weakest). (2) Enriched respiration 12C products are recognized in A. mayaroensis, Gublerina acuta De Klasz, and Heterohelix planata (Cushman). Isotopic trends between samples suggest that photosymbiotic activities varied between localities or during different climate modes, and may have ceased under certain environmental conditions. The appearance of most photosymbiotic species in the late Maastrichtian suggests oligotrophic conditions associated with increased water-mass stratification.