Seawater carbonate chemistry, primary production, biomass and calcification of plankton and bacteria, 2009

Production (abundance and biomass) and net calcification rates of the coccolithophorid Pleurochrysis carterae under different partial pressures of CO2 (pCO2) were examined using short (15, 24 and 39 h), long (7 d) and dark (7 d) incubation experiments. Short incubations were conducted at ambient, 500 and 820 ppm pCO2 levels in natural seawater that was enriched with nutrients and inoculated with P. carterae. Long incubations were conducted at ambient and 1200 ppm pCO2 levels in natural seawater (0.2 µm filtered as well as unfiltered) that was enriched with nutrients and inoculated with P. carterae. Dark incubations were conducted at ambient and 1200 ppm pCO2 in unfiltered seawater that was inoculated with P. carterae. The abundance and biomass of coccolithophorids increased with pCO2 and time. The abundance and biomass of most noncalcifying phytoplankton also increased, and were hardly affected by CO2 inputs. Net calcification rates were negative in short incubations during the pre-bloom phase regardless of pCO2 levels, indicating dissolution of calcium carbonate. Further, the negative values of net calcification in short incubations became less negative with time. Net calcification rates were positive in long incubations during blooms regardless of pCO2 level, and the rate of calcification increased with pCO2. Our results show that P. carterae may adapt to increased (~1200 ppm) pCO2 level with time, and such increase has little effect on the ecology of noncalcifying groups and hence in ecosystem dynamics. In dark incubations, net calcification rates were negative, with the magnitude being dependent on pCO2 levels.

Isotopic composition of water in fog, rain, throughfall and stemflow in the Monte Verde, Costa Rica

Fog deposition, precipitation, throughfall and stemflow were measured in a windward tropical montane cloud forest near Monteverde, Costa Rica, for a 65-day period during the dry season of 2003. Net fog deposition was measured directly using the eddy covariance (EC) method and it amounted to 1.2 ± 0.1 mm/day (mean ± standard error). Fog water deposition was 5-9% of incident rainfall for the entire period, which is at the low end of previously reported values. Stable isotope concentrations (d18O and d2H) were determined in a large number of samples of each water component. Mass balance-based estimates of fog deposition were 1.0 ± 0.3 and 5.0 ± 2.7 mm/day (mean ± SE) when d18O and d2H were used as tracer, respectively. Comparisons between direct fog deposition measurements and the results of the mass balance model using d18O as a tracer indicated that the latter might be a good tool to estimate fog deposition in the absence of direct measurement under many (but not all) conditions. At 506 mm, measured water inputs over the 65 days (fog plus rain) fell short by 46 mm compared to the canopy output of 552 mm (throughfall, stemflow and interception evaporation). This discrepancy is attributed to the underestimation of rainfall during conditions of high wind.

Chemistry of biogenic sediments from the equatorial Pacific

To increase our understanding of the mechanisms that control the distribution of Al and Ti within marine sediment, we performed sequential extractions targeting the chemical signatures of the loosely bound, exchangeable, carbonate, oxide, organic, opal, and residual fraction of sediment from a carbonate-dominated regime (equatorial Pacific) and from a mixed opal-terrigenous regime (West Antarctic Peninsula). We observe a systematic partitioning of Al and Ti between sediment phases that is related to bulk Al/Ti. We show that, where we can quantify an Al(excess) component, the dissolved Al is preferentially affiliated with the oxide fraction, resulting in Al/Ti molar ratios of 500-3000. This is interpreted as the result of surface complexation in the water column of dissolved Al onto oxyhydroxides. We also observe a previously undetected Ti(excess) with as much as 80% of the total Ti in the organic fraction, which is most likely a function of metal-organic colloidal removal from the water column. In samples where the excess metals are obscured by the detrital load, the Al and Ti are almost exclusively found in the residual phase. This argues for the paired removal of Al (preferentially by the oxide component) and Ti (preferentially by the organic component) from the water column by settling particulate matter. This research builds upon earlier work that shows changes in the bulk ratio of Al to Ti in carbonate sediment from the central-equatorial Pacific that coincide with changes in the sedimentary bulk accumulation rate (BAR). The ratios that are observed are as much as three times higher than typical shale values, and were interpreted as the result of scavenging of dissolved Al onto particles settling in the water column. Because this non-terrigenous Al(excess) accounts for up to 50% of the total sedimentary Al inventory and correlates best with BAR, the bulk Al/Ti may be a sensitive tracer of particle flux and, therefore, export production. Because we show that the excess metals are the result of scavenging processes, the bulk Al/Ti may be considered a sensitive proxy for this region.

Late Quaternary planktonic foraminifera of ODP Hole 175-1087A

Planktonic foraminiferal assemblages from the upper Pleistocene part of Hole 1087A (0 to 12.1 meters below seafloor) are investigated to assess the role of global and local climate changes on surface circulation in the southern Benguela region. The benthic stable isotope record indicates that the studied interval is representative of the last four climatic cycles, that is, down to marine isotope Stage (MIS) 12. The species assemblages bear a clear transitional to subpolar character, with Neogloboquadrina pachyderma (d), Globorotalia inflata, and Globigerina bulloides, in order of decreasing abundance, as the dominant taxa. This species association presently characterizes the mixing domain of old upwelled and open ocean waters, seaward of the Benguela upwelling cells. Abundance variation of the dominant foraminiferal species roughly follows a glacial-interglacial pattern down to MIS 8, suggesting an alternation of upwelling strength and associated seaward extension of the belt of upwelled water as a response to global climate changes. This pattern is interrupted from ~250 ka down to MIS 12, where the phase relationship with global climate is ill defined and might be interpreted as a local response of the southern Benguela region to the mid-Brunhes event. Of particular interest is a single pulse of newly upwelled waters at the location of Site 1087 during early MIS 9 as indicated by a peak abundance of sinistral N. pachyderma (s). Variable input of warm, salty Indian Ocean thermocline waters into the southeast Atlantic, a key component of the Atlantic heat conveyor, is indicated by abundance changes of the tropical taxon Globorotalia menardii. From this tracer, we suggest that interocean exchange was hardly interrupted throughout the last 460 k.y., but was most effective at glacial terminations, particularly during Terminations I and II, as well as during the upper part of MIS 12. This maximum input of Indian Ocean waters around the southern tip of Africa is associated with the reseeding of G. menardii in the tropical Atlantic.

Biomass and bioturbation in surface sediments of the Arctic Ocean

Little is known about the benthic communities of the Arctic Ocean's slope and abyssal plains. Here we report on benthic data collected from box cores along a transect from Alaska to the Barents Abyssal Plain during the Arctic Ocean Section of 1994. We determined: (1) density and biomass of the polychaetes, foraminifera and total infauna; (2) concentrations of potential sources of food (pigment concentration and percent organic carbon) in the sediments; (3) surficial particle mixing depths and rates using downcore 210Pb profiles; and (4) surficial porewater irrigation using NaBr as an inert tracer. Metazoan density and biomass vary by almost three orders of magnitude from the shelf to the deep basins (e.g. 47 403 individuals m**-2 on the Chukchi Shelf to 95 individuals m**-2 in the Barents Abyssal Plain). Water depth is the primary determinant of infaunal density, explaining 39% of the total variability. Potential food concentration varies by almost two orders of magnitude during the late summer season (e.g. the phaeopigment concentration integrated to 10 cm varies from 36.16 mg m**-2 on the Chukchi Shelf to 0.94 mg m**-2 in the Siberia Abyssal Plain) but is not significantly correlated with density or biomass of the metazoa. Most stations show evidence of particle mixing, with mixing limited to <=3 cm below the sediment-water interface, and enhanced pore water irrigation occurs at seven of the nine stations examined. Particle mixing depths may be related to metazoan biomass, while enhanced pore water irrigation (beyond what is expected from diffusion alone) appears to be related to total phaeopigment concentration. The data presented here indicate that Arctic benthic ecosystems are quite variable, but all stations sampled contained infauna and most stations had indications of active processing of the sediment by the associated infauna.