Deep-sea Research Part Ii-topical Studies in Oceanography 

About: Deep-sea Research Part Ii-topical Studies in Oceanography is an academic journal published by Elsevier BV. The journal publishes majorly in the area(s): Phytoplankton & Upwelling. It has an ISSN identifier of 0967-0645. Over the lifetime, 4953 publications have been published receiving 250742 citations. The journal is also known as: Topical studies in oceanography.

Climatological mean and decadal change in surface ocean pCO2, and net sea–air CO2 flux over the global oceans

Abstract: A climatological mean distribution for the surface water pCO2 over the global oceans in non-El Nino conditions has been constructed with spatial resolution of 4° (latitude) ×5° (longitude) for a reference year 2000 based upon about 3 million measurements of surface water pCO2 obtained from 1970 to 2007. The database used for this study is about 3 times larger than the 0.94 million used for our earlier paper [Takahashi et al., 2002. Global sea–air CO2 flux based on climatological surface ocean pCO2, and seasonal biological and temperature effects. Deep-Sea Res. II, 49, 1601–1622]. A time-trend analysis using deseasonalized surface water pCO2 data in portions of the North Atlantic, North and South Pacific and Southern Oceans (which cover about 27% of the global ocean areas) indicates that the surface water pCO2 over these oceanic areas has increased on average at a mean rate of 1.5 μatm y−1 with basin-specific rates varying between 1.2±0.5 and 2.1±0.4 μatm y−1. A global ocean database for a single reference year 2000 is assembled using this mean rate for correcting observations made in different years to the reference year. The observations made during El Nino periods in the equatorial Pacific and those made in coastal zones are excluded from the database. Seasonal changes in the surface water pCO2 and the sea-air pCO2 difference over four climatic zones in the Atlantic, Pacific, Indian and Southern Oceans are presented. Over the Southern Ocean seasonal ice zone, the seasonality is complex. Although it cannot be thoroughly documented due to the limited extent of observations, seasonal changes in pCO2 are approximated by using the data for under-ice waters during austral winter and those for the marginal ice and ice-free zones. The net air–sea CO2 flux is estimated using the sea–air pCO2 difference and the air–sea gas transfer rate that is parameterized as a function of (wind speed)2 with a scaling factor of 0.26. This is estimated by inverting the bomb 14C data using Ocean General Circulation models and the 1979–2005 NCEP-DOE AMIP-II Reanalysis (R-2) wind speed data. The equatorial Pacific (14°N–14°S) is the major source for atmospheric CO2, emitting about +0.48 Pg-C y−1, and the temperate oceans between 14° and 50° in the both hemispheres are the major sink zones with an uptake flux of −0.70 Pg-C y−1 for the northern and −1.05 Pg-C y−1 for the southern zone. The high-latitude North Atlantic, including the Nordic Seas and portion of the Arctic Sea, is the most intense CO2 sink area on the basis of per unit area, with a mean of −2.5 tons-C month−1 km−2. This is due to the combination of the low pCO2 in seawater and high gas exchange rates. In the ice-free zone of the Southern Ocean (50°–62°S), the mean annual flux is small (−0.06 Pg-C y−1) because of a cancellation of the summer uptake CO2 flux with the winter release of CO2 caused by deepwater upwelling. The annual mean for the contemporary net CO2 uptake flux over the global oceans is estimated to be −1.6±0.9 Pg-C y−1, which includes an undersampling correction to the direct estimate of −1.4±0.7 Pg-C y−1. Taking the pre-industrial steady-state ocean source of 0.4±0.2 Pg-C y−1 into account, the total ocean uptake flux including the anthropogenic CO2 is estimated to be −2.0±1.0 Pg-C y−1 in 2000.

Global sea-air CO2 flux based on climatological surface ocean pCO2, and seasonal biological and temperature effects

Abstract: Based on about 940,000 measurements of surface-water pCO2 obtained since the International Geophysical Year of 1956–59, the climatological, monthly distribution of pCO2 in the global surface waters representing mean non-El Nino conditions has been obtained with a spatial resolution of 4°×5° for a reference year 1995. The monthly and annual net sea–air CO2 flux has been computed using the NCEP/NCAR 41-year mean monthly wind speeds. An annual net uptake flux of CO2 by the global oceans has been estimated to be 2.2 (+22% or ?19%) Pg C yr?1 using the (wind speed)2 dependence of the CO2 gas transfer velocity of Wanninkhof (J. Geophys. Res. 97 (1992) 7373). The errors associated with the wind-speed variation have been estimated using one standard deviation (about±2 m s?1) from the mean monthly wind speed observed over each 4°×5° pixel area of the global oceans. The new global uptake flux obtained with the Wanninkhof (wind speed)2 dependence is compared with those obtained previously using a smaller number of measurements, about 250,000 and 550,000, respectively, and are found to be consistent within±0.2 Pg C yr?1. This estimate for the global ocean uptake flux is consistent with the values of 2.0±0.6 Pg C yr?1 estimated on the basis of the observed changes in the atmospheric CO2 and oxygen concentrations during the 1990s (Nature 381 (1996) 218; Science 287 (2000) 2467). However, if the (wind speed)3 dependence of Wanninkhof and McGillis (Res. Lett. 26 (1999) 1889) is used instead, the annual ocean uptake as well as the sensitivity to wind-speed variability is increased by about 70%. A zone between 40° and 60° latitudes in both the northern and southern hemispheres is found to be a major sink for atmospheric CO2. In these areas, poleward-flowing warm waters meet and mix with the cold subpolar waters rich in nutrients. The pCO2 in the surface water is decreased by the cooling effect on warm waters and by the biological drawdown of pCO2 in subpolar waters. High wind speeds over these low pCO2 waters increase the CO2 uptake rate by the ocean waters. The pCO2 in surface waters of the global oceans varies seasonally over a wide range of about 60% above and below the current atmospheric pCO2 level of about 360 ?atm. A global map showing the seasonal amplitude of surface-water pCO2 is presented. The effect of biological utilization of CO2 is differentiated from that of seasonal temperature changes using seasonal temperature data. The seasonal amplitude of surface-water pCO2 in high-latitude waters located poleward of about 40° latitude and in the equatorial zone is dominated by the biology effect, whereas that in the temperate gyre regions is dominated by the temperature effect. These effects are about 6 months out of phase. Accordingly, along the boundaries between these two regimes, they tend to cancel each other, forming a zone of small pCO2 amplitude. In the oligotrophic waters of the northern and southern temperate gyres, the biology effect is about 35 ?atm on average. This is consistent with the biological export flux estimated by Laws et al. (Glob. Biogeochem. Cycles 14 (2000) 1231). Small areas such as the northwestern Arabian Sea and the eastern equatorial Pacific, where seasonal upwelling occurs, exhibit intense seasonal changes in pCO2 due to the biological drawdown of CO2.

A new, mechanistic model for organic carbon fluxes in the ocean based on the quantitative association of POC with ballast minerals

Abstract: In simulation studies of the ocean's role in the global carbon cycle, predicting the depth-distribution for remineralization of particulate organic carbon (POC) is of particular importance. Following Sarmiento et al. (Global Biogeochemical Cycles 7 (1993) 417), most simulation models have the power-law curve of Martin et al. (Deep-Sea Research 34 (1987) 267) for this purpose. The Martin et al. curve is an empirical fit to data, most of which is from shallow floating sediment traps. Using such a fit implies that all the information necessary for prediction is contained in the carbon flux itself, so that the organic-carbon flux F OC ( z ) at any depth z can be predicted from the flux of organic carbon F OC ( z 0 ) at some near-surface depth z 0 . Here, we challenge this basic premise, arguing that fluxes of ballast minerals (silicate and carbonate biominerals, and dust) determine deep-water POC fluxes, so that a mechanism-based model of POC flux must simultaneously predict fluxes of both POC and ballast minerals. This assertion is based on the empirical observation that POC fluxes are tightly linked quantitatively to fluxes of ballast minerals in the deep ocean. Here, we develop a model structure that incorporates this observation, and fit this model to US JGOFS EqPac data. This model structure, plus the preliminary parameter estimates we have obtained, can be used to explore the implications of our model in studies of the ocean carbon cycle.

Biogeography, biodiversity and fluid dependence of deep-sea cold-seep communities at active and passive margins

Abstract: To date, several cold-seep areas which fuel chemosynthesis-based benthic communities have been explored, mainly by deployment of manned submersibles. They are located in the Atlantic and in the Eastern and Western Pacific oceans and in the Mediterranean Sea, in depths ranging between 400 and 6000 m in different geological contexts in passive and active margins. Our study is based on a review of the existent literature on 24 deep cold seeps. The geographic distribution of seeps, the variations of origin and composition of fluids, and rates of fluid flow are presented as they are important factors which explain the spatial heterogeneity and the biomass of biological communities. Methane-rich fluid of thermogenic and/or biogenic origin is the principal source of energy for high-productive communities; however, production of sulphide by sulphate reduction in the sediment also has a major role. The dominant seep species are large bivalves belonging to the families Vesicomyidae or Mytilidae. Other symbiont-containing species occur belonging to Solemyidae, Thyasiridae, Lucinidae bivalves, Pogonophora worms, Cladorhizidae and Hymedesmiidae sponges. Most of the symbiont-containing cold-seep species are new to science. Different symbiont-containing species rely on sulphide or methane oxidation, or both, via chemoautotrophic endosymbiotic bacteria. A total of 211 species, from which 64 are symbiont-containing species, have been inventoried. Patterns in biodiversity and biogeography are proposed. A large majority of the species are endemic to a seep area and the symbiont-containing species are mainly endemic to the cold-seep ecosystem. A comparison of species found in other deep chemosynthesis-based ecosystems, hydrothermal vents, whale carcass and shipwreck reduced habitats, reveals from the existing data, that only 13 species, of which five are symbiont-containing species occur, at both seeps and hydrothermal vents. The species richness of cold-seep communities decreases with depth. High diversity compared to that on hydrothermal vent sites is found at several seeps. This may be explained by the duration of fluid flow, the sediment substrate which may favour long-term conditions with accumulation of sulphide and the evolution of cold seeps.

New measurements of phytoplankton and ice algal production in the Arctic Ocean

Abstract: During the Canada/US 1994 Arctic Ocean Section, algal biomass (Chlorophyll a) and primary production were measured in the water column, at the ice-water interface and in the bottom 24 cm of the sea ice along a transect from the Chukchi Sea to the Nansen Basin via the North Pole Algal biomass and primary production were determined for 07-5 urn and > 5 urn size fractions The algal release rate of D014C during incubation was also measured In the Chukchi Sea and in leads of the Makarov and Nansen Basins, total maximum particulate phytoplankton production rates were 2570,73 and 521 mg C m-* day-', respectively At these stations, where ice cover varied from 55 to 90%, large phytoplankton ( > 5 pm) represented 61-98% of the total algal biomass At stations with higher ice coverage (>90%), the total phytoplankton production decreased to 9- 57mgCm-*day-' At these stations, small phytoplankton (07-5 urn) accounted for 59-88% of the total biomass and more than 64% of the total production Along the transect, the percentage of the total phytoplankton production released as extracellular carbon was generally less than 20%, except in the Canadian Basin where it ranged from 31 to 65% Total particulate ice algal production ranged from 05 to 310 mg C m-* day-' and showed maximum rates in the central Arctic Ocean Large cells ( > 5 urn) generally dominated the ice algal community, representing 5&100% of the total biomass and more than 50% of the total production Ice algae released on average 34% of total carbon fixed during the 4-12 h incubation Ice algae contributed on average 57% of the entire primary production (water column + sea ice) in the central Arctic and 3% in the surrounding regions Total primary productivity in the central Arctic Ocean is estimated at 15 g C m-* year-', a value at least 10 times higher than previously reported The difference between estimates is due in part to the previously unmeasured contribution of the particulate production by ice algae and the release of DOC by both ice and pelagic algae 0 1998 Elsevier Science Ltd All rights reserved