Mary-Lynn Dickson

In vitro O2 fluxes compared with 14C production and other rate terms during the JGOFS Equatorial Pacific experiment

We report rates of gross and net O2 production measured in vitro during JGOFS cruises in the equatorial Pacific in spring and fall, 1992. We scale O2 productivities to net and gross C production. We then compare the calculated rates with 14C production and with new/export production measured by various techniques. 14C productivities in samples incubated for 24 h are about 45% of gross carbon production rates calculated from gross O2 production. The difference is compatible with expected rates of the Mehler reaction, photorespiration, excretion, and community mitochondrial respiration. 14C production rates are similar to net carbon production rates in the upper half of the euphotic zone. At lower irradiances, where net C production can be zero or less, 14C productivities lie between net community production and gross primary production. Net carbon production rates in vitro are a factor of =4–20 times greater than estimates from drifting sediment trap and tracer transport studies. This difference probably reflects anomalous accumulation of POC in bottles because of the exclusion of grazers.

Constraining bacterial production, conversion efficiency and respiration in the Ross Sea, Antarctica, January–February, 1997

Bacteria consume dissolved organic carbon at rates averaging about 50% of primary production across a wide spectrum of marine ecosystems. However, total utilization rates are poorly constrained due to a lack of data on conversion e

The effect of marginal ice-edge dynamics on production and export in the Southern Ocean along 170°W

ciencies and/or bacterial respiration rates. We estimated total community dark respiration rates (DCR) from in vitro oxygen utilization and estimated bacterial production from 3H-leucine incorporation during January}February 1997 in the Ross Sea, Antarctica. Bacterial respiration rates (BR) were estimated by assuming that BR was less than some fraction of DCR, and by choosing values for the bacterial growth e

Gas exchange, dispersion, and biological productivity on the West Florida Shelf: Results from a Lagrangian Tracer Study

ciency. By comparing these derived bacterial respiration rates with the DCR we were able to constrain conversion e

Production and respiration rates in the Arabian Sea during the 1995 Northeast and Southwest Monsoons

ciency and bacterial production within various bounds. Bacterial biomass was 10% of phytoplankton stocks, and we considered that bacterial respiration was a similar fraction of the total respiration. To meet this constraint bacterial production rates likely averaged about 5}10% of the net community production, and conversion e

Plankton community composition, production, and respiration in relation to dissolved inorganic carbon on the West Florida Shelf, April 1996

ciencies had to be in the range of 35}45%, similar to independent discrete measurements made during the summer season on this cruise. Dark respiration rates are an absolute constraint on the estimates of bacterial carbon demand. A low value of the leucine conversion factor (1.5 kgC mol~1) was required to meet this strong constraint. ( 2000 Elsevier Science Ltd. All rights reserved.

Climate correlations between Greenland and Antarctica during the past 100,000 years

We present a synthesis of the rates of gross, new, net andprimary production along with particulate organic carbon (POC) flux at 100 m from four cruises along 1701W in the Southern Ocean. Concurrent satellite pigment data, a primary productivity model, and a nitrate mass balance are used to extrapolate daily production estimates in space and time to seasonal and annual rates. From this analysis, we gain a better understanding of the timing, magnitude and impact of the phytoplankton blooms in this region. One of the dominant features with respect to plankton biomass is the association of high chlorophyll levels with the retreat of the sea ice which begins in October just south of the Polar Front. Our primary production model and satellite pigment data suggest higher production and flux levels characterize the marginal ice zone than previous estimates. Elevatedrates of new production in ice impactedregions are restrictedto relatively short periods following retreat of the ice edge. Export is found to lag the onset of production by up to 1 month. The ratio of POC flux at 100 m to primary production when averaged over the entire season is quite high, increasing from 15% to 25% in the Subantarctic zones to 35–40% near the Polar Front andas high as 50–65% in the southernmost stations, just north of the Ross Sea gyre. Comparisons of phytoplankton community structure andFe stress indicators suggest that blooms at the Polar Front are initially dominated by large centric diatoms, but are replaced by smaller pennate diatom and non-diatom species as Fe levels decrease. Further south, where Fe levels are never as high and large diatoms are not found, we still observe relatively high biomass and elevated production rates andPOC fluxes d uring the short growing season. r 2003 Elsevier Science Ltd. All rights reserved.

Vertical budgets for organic carbon and biogenic silica in the Pacific sector of the Southern Ocean, 1996–1998

A Lagrangian tracer study was performed on the west Florida shelf in April 1996 using deliberately injected trace gases. Although such studies have been performed previously, this work is the first where the deliberate tracers, in conjunction with carbon system parameters, are used to quantify changes in water column carbon inventories due to air-sea exchange and net community metabolism. The horizontal dispersion and the gas transfer velocity were determined over a period of 2 weeks from the change in both the concentrations and the concentration ratio of the two injected trace gases, sulfur hexafluoride (SF6) and helium-3 (³He). The second moment of the patch grew to 1.6 × 10³ km² over a period of 11 days. The gas transfer velocity, normalized to CO2 exchange at 20°C, was 8.4 cm hr−1 at an average wind speed, U10, of 4.4 m s−1 for the duration of the experiment, which is in good agreement with empirical estimates. Remineralization rates exceeded productivity, causing an increase in dissolved inorganic carbon of about 1 µmol kg−1 day−1 in the water column. During this period of senescence, 80% of the increase in inorganic carbon is attributed to community remineralization and 20% due to invasion of atmospheric CO2.

Ratios of Si, C and N uptake by microplankton in the Southern Ocean

Abstract In this paper we examine the relationships among oxygen, carbon and nitrogen production and respiration rate measurements made in the Arabian Sea during the 1995 Northeast (NEM) and Southwest (SWM) Monsoons. Increased biological production characterized the SWM, with rates 12–53% higher than the NEM. In most cases, we found remarkable similarity in production rates during the two monsoons and an absence of strong spatial gradients in production between nearshore and offshore waters, especially during the SWM. Daily 14C and total 15N production underestimated gross C production, and at the majority of stations 14C and total 15N production were either the same as net C production or between gross and net C production. Moreover, new production (15NO3), scaled to carbon, was substantially less than net C production. Approximately 50% of the PO14C was metabolized during the photoperiod, with smaller losses (7–11%) overnight. The simplest explanation for the discrepancy between gross and total 15N production and between net C and new production was the loss of 15N-labeled particulate matter as dissolved organic matter. Partitioning of metabolized gross C production into respiratory and dissolved pools showed distinct onshore–offshore distributions that appeared to be related to the composition of the phytoplankton assemblage and probably reflected the trophodynamics of the ecosystem. The percentage of gross C production released as dissolved organic carbon (DOC) was highest in the nearshore waters where diatoms dominated the phytoplankton assemblage, while community respiration was a more important fate for production further offshore where picoplankton prevailed. In general, stations that retained more gross C production as net production (i.e., high net C/gross C ratios) had higher rates of DOC production relative to community respiration. Locations where community respiration exceeded DOC production were characterized by low rates of net C production and had low net C/gross C ratios. In those ecosystems, less net C production was retained because higher metabolic losses reduced gross C production to a greater extent than at the more productive sites.

Carbon cycling in primary production bottle incubations: inferences from grazing experiments and photosynthetic studies using 14C and 18O in the Arabian Sea

In April 1996 the Florida Shelf Lagrangian Experiment examined dissolved inorganic carbon (DIC) dynamics on the West Florida Shelf. DIC concentrations increased over 2 weeks at an average rate of 1 μmol kg−1 d−1 in a patch of the intentionally released tracers sulfur hexafluoride (SF6) and helium 3 (3He). Approximately 20% of the increase was due to air-sea exchange with the remaining 80% attributed to plankton respiration [Wanninkhof et al., 1997]. Here we present particulate matter concentrations, phytoplankton production, and community respiration rates from the tracer patch that suggest that heterotrophs dominated the community after the termination of a spring bloom. During the experiment, chlorophyll a and phaeopigment concentrations declined from >1.5 to 200 and particulate organic nitrogerr.chlorophyll a >100, suggests that phytoplankton were a minor component of the plankton biomass. Rates of daily gross primary production estimated by the H2 18O method averaged 69±5 mmol C m−2 d−1 (n = 3) while dark respiration rates, estimated from dark bottle incubations, were approximately - 40±3 mmol C m−2 d−1. Net community production rates (6±6 mmol C m−2 d−1) were much lower than respiration rates. Thus respiration rates nearly balanced phytoplankton production. Light respiration rates were estimated from gross production minus net community production (−51±8 mmol C m−1 d−1) and exceeded dark respiration. Plankton community respiration rates, corrected for autotrophic carbon fixation, were more than sufficient to account for the observed increase of DIC within the tracer patch.