A new vision of ocean biogeochemistry after a decade of the Joint Global Ocean Flux Study (JGOFS)

The Joint Global Ocean Flux Study (JGOFS) has completed a decade of intensive process and time-series studies on the regional and temporal dynamics of biogeochemical processes in five diverse ocean basins. Its field program also included a global survey of dissolved inorganic carbon (DIC) in the ocean, including estimates of the exchange of carbon dioxide (CO2) between the ocean and the atmosphere, in cooperation with the World Ocean Circulation Experiment (WOCE). This report describes the principal achievements of JGOFS in ocean observations, technology development and modelling. The study has produced a comprehensive and high-quality database of measurements of ocean biogeochemical properties. Data on temporal and spatial changes in primary production and CO2 exchange, the dynamics of of marine food webs, and the availability of micronutrients have yielded new insights into what governs ocean productivity, carbon cycling and export into the deep ocean, the set of processes collectively known as the "biological pump." With large-scale, high-quality data sets for the partial pressure of CO2 in surface waters as well for other DIC parameters in the ocean and trace gases in the atmosphere, reliable estimates, maps and simulations of air-sea gas flux, anthropogenic carbon and inorganic carbon export are now available. JGOFS scientists have also obtained new insights into the export flux of particulate and dissolved organic carbon (POC and DOG), the variations that occur in the ratio of elements in organic matter, and the utilization and remineralization of organic matter as it falls through the ocean interior to the sediments. JGOFS scientists have amassed long-term data on temporal variability in the exchange of CO2 between the ocean and atmosphere, ecosystem dynamics, and carbon export in the oligotrophic subtropical gyres. They have documented strong links between these variables and large-scale climate patterns such as the El Nino-Southern Oscillation (ENSO) or the North Atlantic Oscillation (NAO). An increase in the abundance of organisms that fix free nitrogen (N-2) and a shift in nutrient limitation from nitrogen to phosphorus in the subtropical North Pacific provide evidence of the effects of a decade of strong El Ninos on ecosystem structure and nutrient dynamics. High-quality data sets, including ocean-color observations from satellites, have helped modellers make great strides in their ability to simulate the biogeochemical and physical constraints on the ocean carbon cycle and to extend their results from the local to the regional and global scales. Ocean carbon-cycle models, when coupled to atmospheric and terrestrial models, will make it possible in the future to predict ways in which land and ocean ecosystems might respond to changes in climate

Century- to milliennial-scale sedimentological-geochemical records of glacial-Holocene sediment variations from the Barra Fan (NE Atlantic).

The Barra Fan, located at the continental margin of NW Scotland, offers a unique possibility to retrieve records of exceptional high resolution to obtain climate records on a century-millennial timescale. We used a sedimentological-geochemical approach to examine the sediment variations that reflect the palaeoceanography and climate history of the area. Inorganic chemistry combined with micropalaeontology reveals trends and changes in NE Atlantic palaeoceanography and northwest European climate at the sub-Milankovitch frequency. This study builds on results from two British Geological Survey cores and one giant piston core (Core 57/-11/59, Core 56/-10136 and Images Core MD95-2006) that were obtained during the NEAPACC (NE Atlantic Palaeoceanography, Special Topic NERC) phase. Geochemical records of lithogenic input fluctuate rapidly and their patterns parallel sea surface temperature and particle size records. The cold periods are characterized by increased clay input compared to the warm periods. The Younger Dryas period and other prominent periods such as the equivalent of Heinrich Event 1, show extremely expanded sections up to several metres in thickness. Enhancement of accumulation rates in the glacial section is due to the influence of downslope sedimentation, meltwater deposition; and large-scale currents redistributing the sediment along the upper slope. The radiochemical tracer (excess Th-230) shows that major shifts in terrigenous sediment supply were extremely rapid over the last 15 ka. The shifts in terrigenous supply occurred over time-spans of less than a century. Century-scale events of lithogenic input can be visually correlated to other North Atlantic climate records such as the GISP2 Greenland ice core delta(18)O record for the last 15 ka, although the resolution of radiocarbon dating of these events in the sediments is not sufficiently precise to verify that the visual correlations are correct. The particle flux and biogenic records show sawtooth-shaped cycles opposite to the Dansgaard-Oeschger cycles.</p

Historical storage budgets of organic carbon, nutrient and contaminant elements in saltmarsh sediments: Biogeochemical context for managed realignment, Humber Estuary, UK

Biogeochemical data from Welwick marsh (Humber Estuary, UK), an actively accreting saltmarsh, provides a decadal–centennial-scale natural analogue for likely future biogeochemical storage effects of managed realignment sites accreting either intertidal muds or saltmarsh. Marsh topographic profiles and progradation history from aerial photographs were combined with 137Cs and niobium contamination history to establish and verify chronology and sediment mass accumulation. These data, combined with down-core measurements of particulate organic carbon (Corg), organic nitrogen (Norg), particle reactive phosphorus and selected contaminant metal (Zn, Pb, Cu, As and Nb) contents were then used to calculate sediment and chemical storage terms and to quantify changes in these over time. These data are used to help predict likely future biogeochemical storage changes at managed realignment sites in the estuary. The net effect of returning some 26 km2 of reclaimed land to intertidal environments now (about 25% of the maximum possible realignment storage identified for the estuary) could result in the storage of some 40,000 tonnes a- 1 of sediment which would also bury about 800 tonnes a- 1 of Corg and 40 tonnes a- 1 of Norg. Particulate contaminant P burial would be around 25 tonnes a- 1 along with ~ 6 tonnes a- 1 contaminant Zn, 3 tonnes a- 1 contaminant Pb, and ~ 1 tonnes a- 1 contaminant As and Cu. The study also shows that reclamation activities in the outer estuary since the mid-1700s has prevented, in total, the deposition of about 10 million tonnes of sediment, along with 320,000 tonnes of Corg and 16,000 tonnes of Norg. The study provides a mid-1990s baseline against which future measurements at the site can determine changes in burial fluxes and improvement or deterioration in contaminant metal contents of the sediments. The data are directly relevant for local managed realignment sites but also broadly indicative for sites generally on the European North Sea Coast