Dissolved organic carbon production by microbial populations in the Atlantic Ocean

Abstract

Dissolved organic carbon (DOC) production by microbial populations was measured at 19 stations in the Atlantic Ocean to quantify the fraction of photoassimilated carbon that flows through the dissolved organic pool at basin scale and to assess the relationship between the percentage of DOC production, phytoplankton size structure, and rates of net community production. Experiments were conducted during four cruises carried out between May 1998 and October 1999, covering three upwelling regions: Benguela (SW Africa), Mauritania (NW Africa) and NW Spain, and the oligotrophic North Atlantic subtropical gyre between 30ЊN and 36ЊN. Photic zone integrated particulate organic carbon (POC) production rates ranged from 10 to 1,178 mg C m Ϫ2 h Ϫ1, thus covering a wide productivity spectrum. The percentage of DOC production with respect to total integrated primary production ranged from 4 to 42%, being larger in oligotrophic, picoplankton-dominated waters, where a balanced metabolism of the microbial community was observed, than in productive, net autotrophic waters, where large-sized cells formed the bulk of the phytoplankton biomass. A highly significant relationship was calculated between DOC and POC production rates in upwelling conditions. By contrast, the relationship between these variables in oligotrophic environments was weak, which suggests that different processes could be controlling the release of dissolved organic matter in productive and unproductive waters.Dissolved organic matter (DOM) is one of the least understood pools of marine matter and represents a major reservoir of organic carbon in the ocean. A large fraction of the dissolved organic carbon (DOC) present in the ocean ultimately derives from primary producers. However, a great deal of controversy still exists on the ecological significance and the ultimate control of DOC production in the ocean.The magnitude of DOC-related fluxes remains still largely uncertain, especially in oligotrophic regions. The high rates of DOC uptake by heterotrophic bacteria in relation to primary production recently measured in unproductive waters (e.g., Hansell et al. 1995;del Giorgio et al. 1997), largely justifies the growing biogeochemical interest of measuring and modeling DOC production in planktonic ecosystems.Initially, the radioactive carbon method for primary production estimation was modified for the measurement of direct excretion of dissolved organic compounds from algal cells. More recently, it has been recognized that several processes, besides direct excretion from intact algal cells, are 1 Corresponding author (eteira@uvigo.es). AcknowledgmentsWe thank G. Tilstone, B. Mouriño, C. Cariño, and C. Robinson for their contributions to the collection of data. Thanks to P. J. le B. Williams for the generous loan of analytical equipment used on the AMT-6 cruise. We are indebted to the captain and crew of research vessels, as well as to all the colleagues on board during the four cruises. We appreciate the comments of two anonymous referees, which improv...

Carbon‐nitrogen coupling and algal‐bacterial interactions during an experimental bloom: Modeling a 13C tracer experiment

“…This variability has been related to many factors, including nutrient availability, phytoplankton size, and net community production (Teira et al 2001). It is unclear whether the increase in DOC release under nutrient-stressed conditions is caused by the preponderance of small cells with higher surface : volume ratios and, therefore, a higher capacity of passive leakage of DOC (Bjørnsen 1988), to the physiological condition of the algae (Dubinsky and Berman-Frank 2001), or a combination of both.…”

The magnitude of spring bacterial production in the North Atlantic Ocean

“…Baines and Pace (1991) reviewed 16 studies and 225 measurements of PER in marine and freshwater systems and found that PER averaged 13% of particulate PP (95% confidence intervals 2-50%). Recently Teira et al (2001) made a comprehensive series of measurements along a productivity gradient off the Spanish Coast, finding PER was a mean of 7% of PP in the coastal upwelling area and 28% in offshore, oligotrophic waters. Thus recent data sets as well as earlier reviews suggest that while values upward of 40% do occur, mean values are usually in the range of 10-20% of the particulate production rates normally measured with 14 C.…”

Dissolved organic matter (DOM) release by phytoplankton in the contemporary and future ocean

“…Data from the Atlantic Ocean show water temperature affects phytoplankton cell size, with picophytoplankton becoming more dominant at warmer temperatures . Communities dominated by picophytoplankton in the Atlantic Ocean have higher PER than phytoplankton communities dominated by larger cells (Teira et al, 2001a(Teira et al, , 2001b. However, in the field it is difficult to uncouple nutrient limitation and temperature effects.…”

“…However, this is not the only factor, as PER is also generally higher in situ at upwelling locations, where nutrients are available, compared with laboratory monocultures. Shortterm incubations using water collected in situ include protozoan grazing and viral lysis, processes that are usually absent in phytoplankton cultures (Nagata, 2000;Teira et al, 2001a). In low biomass locations, such as the oligotrophic ocean, methodological constraints may lead to an overestimation of PER based on incubations using 14 C, as the signal is relatively low compared with the noise, and this may be a concern in the interpretation of some of the early measurements (Williams, 1990).…”

“…It is difficult to compare the in situ studies presented in Table 1 due to the wide range of protocols used to obtain the data. For example, Wetz & Wheeler (2003) conducted on-deck incubations of 20 litres, which were sampled each day for 7 days, whereas Teira et al (2001a) measured DOC release in 30-ml samples after an on-deck incubation time of 2 hours. These differences suggest that an inter-comparison of methods commonly used to measure PER would be a valuable exercise, potentially leading to a standard protocol and enabling direct comparisons between datasets collected by different groups at different times and locations.…”