Biogeochemical Controls and Feedbacks on Ocean Primary Production

Abstract

Changes in oceanic primary production, linked to changes in the network of global biogeochemical cycles, have profoundly influenced the geochemistry of Earth for over 3 billion years. In the contemporary ocean, photosynthetic carbon fixation by marine phytoplankton leads to formation of approximately 45 gigatons of organic carbon per annum, of which 16 gigatons are exported to the ocean interior. Changes in the magnitude of total and export production can strongly influence atmospheric CO2 levels (and hence climate) on geological time scales, as well as set upper bounds for sustainable fisheries harvest. The two fluxes are critically dependent on geophysical processes that determine mixed-layer depth, nutrient fluxes to and within the ocean, and food-web structure. Because the average turnover time of phytoplankton carbon in the ocean is on the order of a week or less, total and export production are extremely sensitive to external forcing and consequently are seldom in steady state. Elucidating the biogeochemical controls and feedbacks on primary production is essential to understanding how oceanic biota responded to and affected natural climatic variability in the geological past, and will respond to anthropogenically influenced changes in coming decades. One of the most crucial feedbacks results from changes in radiative forcing on the hydrological cycle, which influences the aeolian iron flux and, in turn, affects nitrogen fixation and primary production in the oceans.

Biological Oceanography by Remote Sensing

“…1 Gt C. This implies that the phytoplankton biomass turns over approximately once per week on average. 44 This is consistent with the fact that the phytoplankton lifecycle is relatively short, of the order of a day.…”

“…39,44 Both of the approaches discussed above rely on more than just the satellite data to obtain these estimates. Neither method is able to distinguish between new and regenerated production, which it is necessary to do in studying carbon fluxes into the ocean (section 4.2).…”

Respiration in the mesopelagic and bathypelagic zones of the oceans

“…Our review indicates that the sum of the above four carbon inputs amounts to 1.5-1.6 Pmol C a −1 , a value close to some recent estimates of new production (Sambrotto et al 1993;Falkowski et al 1998), but somewhat below the estimates of export production proposed recently by del Giorgio and Duarte (2002;2.3 Pmol C a −1 ). Uncertainties in the estimates of the above fluxes could lead to differences between estimates of new production and export biogenic fluxes.…”

“…Since their calculations are based on the magnitude of new production, evidence for a higher value of new production (e.g. 1.3 Pmol C a −1 ; Sambrotto et al 1993;Falkowski et al 1998) would increase the total calculated export by a factor of 2. Arístegui et al (2002a) compiled a large dataset on the relationship between DOC concentration and apparent oxygen utilization (AOU)-the oxygen anomaly with respect to the dissolved oxygen saturation levels-from various oceans.…”

The benthic macrofauna from the Lower Maastrichtian chalk of Kronsmoor (northern Germany, Saturn quarry): taxonomic outline and palaeoecologic implications

“…Today, the relatively small shelf seas are characterized by high biological productivity (e.g., Falkowski et al 1998;Thomas et al 2004), suggesting that primary productivity in shelf seas should have been even more important during greenhouse worlds of the geological past when large, shallow epicontinental seas, such as the Late Cretaceous Chalk Sea, existed. During the Late Cretaceous, it is probable that no boundaries were present between the shelf areas and the pelagic realm (shelf fronts) due to high sea-level stands (Hay 1995(Hay , 2008, in contrast to the present-day situation.…”