Is pore water oxygen content decoupled from productivity on the California Margin? Trace element results from Ocean Drilling Program Hole 1017E, San Lucia slope, California

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95250/1/palo1223.pd

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

Post-glacial depositional environments in a mid-high latitude glacially-overdeepened sea loch, inner Loch Etive, western Scotland

A high-resolution seismic and gravity coring survey has been conducted on inner, and part of outer Loch Etive, a 30 km long, 150 m deep sea loch on the west coast of Scotland, The seismic reflection profiles reveal a 30-60 in thick sediment pile that has accumulated on the floor of the loch since the last (Younger Dryas stadial) glacial re-advance 11-10 ka BP. Four seismic facies have been identified grouped into two seismic sequences, A and B, which are separated by a distinct reflector termed 'El'. A highly reflective facies is interpreted as direct river input, an acoustically well-laminated, draped facies interpreted as fine-grained river sediments and a well-laminated to transparent facies interpreted as glaciomarine and glaciolacustrine. Throughout the loch, methane gas-rich sediments occur producing a chaotic seismic facies. The transition from glacially-influenced to river-dominated deposition is displayed by the seismic reflector El. Core analysis identified eight lithofacies, The oldest sediments are grey muddy sands and olive sandy silts, overlain by younger laminated greeny-grey muddy sand and greeny-grey and greeny-black homogeneous watery sandy mud. Abundant shell material is present throughout, notably the bivalve Arctica islandica, from which a C-14 age of 9490+/-90 yr BP was obtained from the laminated greeny-grey muddy sands. The sediments are interpreted as being of glaciomarine and glaciolacustrine (Younger Dryas to early-mid Holocene) and more modern riverine-derived origin (mid-latest Holocene). (C) 2002 Elsevier Science B.V.. All rights reserved.</p