Increasing quantities of atmospheric anthropogenic fixed nitrogen entering the open ocean could account for up to about a third of the ocean's external (nonrecycled) nitrogen supply and up to approximately 3% of the annual new marine biological production, approximately 0.3 petagram of carbon per year. This input could account for the production of up to approximately 1.6 teragrams of nitrous oxide (N2O) per year. Although approximately 10% of the ocean's drawdown of atmospheric anthropogenic carbon dioxide may result from this atmospheric nitrogen fertilization, leading to a decrease in radiative forcing, up to about two-thirds of this amount may be offset by the increase in N2O emissions. The effects of increasing atmospheric nitrogen deposition are expected to continue to grow in the future.

Measurements of benthic foraminiferal cadmium:calcium (Cd/Ca) have indicated that the glacial-interglacial change in deep North Pacific phosphate (PO(4)) concentration was minimal which has been taken by some, workers as a sign that the biological pump did not store more carbon in the deep glacial ocean. Here we present sedimentary redox-sensitive trace metal records from Ocean Drilling Program (ODP) Site 882 (NW subarctic Pacific, water depth 3244 m) to make inferences about changes in deep North Pacific oxygenation and thus respired carbon storage - over the past 150,000 yr. These observations are complemented with biogenic barium and opal measurements as indicators for past organic carbon export to separate the influences of deep-water oxygen concentration and sedimentary organic carbon respiration on the redox state of the sediment. Our results suggest that the deep subarctic Pacific water mass was deleted in ox en during glacial maxima, though it was not anoxic. We reconcile our results with the existing benthic foraminiferal Cd/Ca by invoking a decrease in the fraction of the deep ocean nutrient inventory that was preformed, rather than remineralized. This change would have corresponded to an increase in the deep Pacific storage of respired carbon, which Would have lowered atmospheric carbon dioxide (CO(2)) by sequestering CO(2) away from the atmosphere and by increasing ocean alkalinity through a transient dissolution event in the deep sea. The magnitude of change in preformed nutrients suggested by the North Pacific data Would have accounted for a majority of the observed decrease in glacial atmospheric PCO(2). (c) 2008 Elsevier B.V. All rights reserved.

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During deglaciation at ∼17 ka the intensity and footprint of the oxygen minimum zone (OMZ) increased in the Eastern Tropical North Pacific (ETNP) before a subsequent expansion on the California Margin. Evidence for the earlier increase is found in trace metal concentrations, lamination preservation and δ15N values from cores located between 540–750 m water depth in the Gulf of Tehuantepec, Southern Mexico. These results differ from similar proxies found even 5°N of the site, where there is evidence for OMZ changes related to rapid climate change in the Northern Hemisphere. Instead, OMZ expansion in the Gulf was contemporaneous with changes in sea ice extent and zonal wind shifts around Antarctica, pointing to Subantarctic Mode Water and Antarctic Intermediate Water as likely sources of oxygen‐depleted water. These observations reinforce the importance of the Southern Ocean as a primary modulator of northern hemisphere ocean climate, as far as 15°N in the ETNP.

Trace element evidence from the California Margin (Ocean Drilling Program Hole 1017E) shows significant changes in sediment redox chemistry at intermediate water depths over the last 60 kyr. The influence of export production on intermediate water oxygen content can be distinguished from lateral ventilation through comparisons among proxies representing export production flux (percent Corg) and sediment‐surface (I/Br) and pore water (Mo, Ag, Cd, Re, and U) oxygenation proxies. Sulfate reduction within the uppermost sediment column occurred during late Quaternary interstadials and the Holocene, indicating reduced intermediate water ventilation. However, sulfate reduction was most intense during major interstadials when productivity was enhanced. Decoupling between export production and pore water oxygen content is demonstrated during deglaciation when the sediment pore water oxygen content increases without a corresponding reduction in export productivity. Thus both export production and intermediate water ventilation play a role in oxygen minimum zone processes on the California Margin.

Since the first evidence of low algal productivity during ice ages in the Antarctic Zone of the Southern Ocean was discovered, there has been debate as to whether it was associated with increased polar ocean stratification or with sea-ice cover, shortening the productive season. The sediment concentration of biogenic barium at Ocean Drilling Program site 882 indicates low algal productivity during ice ages in the Subarctic North Pacific as well. Site 882 is located southeast of the summer sea-ice extent even during glacial maxima, ruling out sea-ice-driven light limitation and supporting stratification as the explanation, with implications for the glacial cycles of atmospheric carbon dioxide concentration.

Application of a high‐resolution multiproxy approach to a sedimentary section drilled at Ocean Drilling Program Site 1017, located under a highly active upwelling cell off Point Conception, California, provides clear evidence for surface ocean productivity shifts on submillennial timescales during the last 60 kyr. The proxies include bulk‐sediment major and minor elements, organic carbon and carbonate concentrations, δ15N, and planktonic foraminiferal species assemblage and carbon isotope determinations. The collective results demonstrate that marine productivity in this area was not simply linearly related to cold and warm cycles except during the millennial‐scale climate oscillations of marine isotope stage (MIS) 3. During that interval, the upwelling cell and resulting high productivity were active during warm interstadial events and were largely inactive during cool stadial events. However, the Last Glacial Maximum was also relatively productive. Productivity increased dramatically during the Bølling warm interval, while the Ållerød and Younger Dryas were much less productive. High coccolithophorid abundance commenced during the earliest Holocene after 10 ka. The complexity of the productivity response was probably related to interplay between local winds, as well as California Undercurrent strength.

The cycling of carbon between the atmosphere, ocean and continents controls the concentration of atmospheric CO2(pCO2), which in turn impacts the earth’s radiation balance. Correlations between the concentration of atmospheric pCO2 measured in air bubbles in ice cores with climatic indices such as inferred global temperature (Chapter 3, Figure 4.3) strongly suggest that some link exists between pCO2, “greenhouse” warming and global climate (Shackleton 2000, and others). Late Quaternary climatic variability occurs predominantly at the 100 ky frequency associated with orbital eccentricity, ε. Since changes in e result in relatively small changes in incoming solar radiation, non-linear internal feedback mechanisms must be invoked to explain climate variations at this frequency. In this context, the rapid collapse but slow growth of northern hemisphere continental ice sheets has often been suggested as an important influence (Imbrie and Imbrie 1980).

Sediments on the Namibian Margin in the SE Atlantic between water depths of ∼1000 and ∼3600 m are highly enriched in hydrocarbon‐prone organic matter. Such sedimentation has occurred for more than 2 million years and is geographically distributed over hundreds of kilometers along the margin, so that the sediments of this region contain a huge concentrated stock of organic carbon. It is shown here that most of the variability in organic content is due to relative dilution by buried carbonates. This reflects both export productivity and diagenetic dissolution, not differences in either water column or bottom water anoxia and related enhanced preservation of organic matter. These observations offer a new mechanism for the formation of potential source rocks in a well‐ventilated open ocean, in this case the South Atlantic. The organic richness is discussed in terms of a suite of probable controls including local wind‐driven productivity (upwelling), trophic conditions, transfer efficiency, diagenetic processes, and climate‐related sea level and deep circulation. The probability of past occurrences of such organic‐rich facies in equivalent oceanographic settings at the edge of large oceanic basins should be carefully considered in deep offshore exploration.

Paleoclimatic research has revealed an astonishing picture of past changes in the earth system. Over the last 2 million years, climate has varied widely from ice ages to warm interglacials. Between these extremes global sea-level varied by up to 130 m, alternately exposing and submerging land bridges that provided gateways between continents for the migration of early humans. Ice sheets grew to such an enormous size, they depressed the earth’s crust under their weight and forced airmasses around them. So much water was sequestered on the continents that the chemical composition of the oceans was altered, affecting all the organisms that lived in the seas. As the ice sheets grew, the world’s terrestrial and marine ecosystems changed, in both distribution and composition. Continental interiors became drier, wind speeds increased and large areas of wind-blown loess accumulated. As ecosystems were altered, the composition of the atmosphere changed repeatedly, with low levels of important greenhouse gases during glacial episodes and higher levels in interglacial periods.

Concentration and mass accumulation rate profiles from Southeastern Atlantic sediment cores located off Namibia show that an exceptional episode in benthic carbonate dissolution occurred during early glacial isotope stage 6 (substages 6.6 and 6.5) between about 186 000 and 170 000 yr BP. Although this episode is restricted to or is more pronounced in this region than in other areas of the Atlantic Ocean, its exceptional character with respect to older and younger climatic episodes at the same site cannot be fully explained by local factors alone, but requires a combination of local and global influences. The onset of the carbonate dissolution episode is related to a more efficient transfer of organic matter from surface eutrophic areas to the lower and is due to low sea level, while its termination relates to a change in either global ocean alkalinity or bottom water circulation. An evaluation of the magnitude of this local carbonate dissolution episode suggests that its contribution to a global alkalinity change may have been significant. Carbonate dissolution was probably amplified by stronger upwelling activity of the Benguela System linked to an exceptional northern excursion of the boreal summer ITCZ during early glacial isotope stage 6. This low latitude global link-age may explain how this carbonate dissolution event as well as other 'anomalies' observed for early stage 6, like an important Dole effect minimum or a 'cold' Mediterranean sapropel, are related. (C) 2002 Elsevier Science B.V. All rights reserved.

Regularly increasing radiocarbon age–depth profiles and near-constant sediment composition with depth have demonstrated that sediment accumulation has been relatively constant during the late Holocene at two north-east Atlantic sites on Rockall Bank and Feni Drift (UK Benthic Boundary Layer Experiment sites). In such a quasi-steady state situation, the geochemical responses to early diagenesis of the redox-sensitive elements Cd, Mn, Mo, Re, Se and U are readily discerned through changes in element concentrations with depth. Collectively, a colour change in the sediments, surficial MnOx-enriched layers and 210Pbexcess profiles allow an estimate of the mean position of the oxic–post-oxic boundary in the sediments at both sites. This boundary is situated deeper than the 210Pbexcess surface mixed layer but shallower than the 14C surface mixed layer which represent mixing on 102 and 103 year time scales, respectively. This implies that the well-defined surface MnOx enrichment and its associated 226Ra and Mo fractions must have been efficiently recycled first by downwards mixing into anoxic conditions, and then by subsequent reduction and diffusive migration back up into oxic conditions. This occurs in <40 years at the Feni Drift site and in <103 years at the Rockall Bank site. Authigenic enrichments of Se, Cd and U are evident immediately below the oxic–post-oxic boundary, although Re enrichment does not occur until a few centimetres deeper. The long-term fluxes of authigenic Se, Cd, U and Re uptake are evaluated with steady-state assumptions. While diffusion from bottom waters can supply sufficient Se, U and Re, an additional source (likely Corg) is required for Cd.

A major obstacle to producing reliable predictions of climate change and its impacts is a lack of data on time scales longer than the short instrumental record. Recently initiated climate observation programs will need to be continuously operated for at least 50 years before they begin to provide information that is relevant to this problem. In contrast, natural archives of past climate variability can provide relevant information now. Unfortunately, some of the most valuable paleoclimate archives are being rapidly destroyed, largely as a result of human influences (see the related News of the Week article in this issue by Koenig). We cannot afford such an irreversible loss. The Past Global Changes (PAGES) program of the International Geosphere-Biosphere Programme therefore calls for scientists, funding agencies, and institutional partners to establish immediately a coordinated international Global Paleoclimate Observing System (GPOS) to complement the Global Climate, Terrestrial, and Ocean Observing Systems (GCOS, GTOS, and GOOS, respectively) that focus only on contemporary observations. An example of the loss of paleoarchives is the rapid retreat of alpine glaciers in the tropics and temperate latitudes. Ice cores from such glaciers have been used to reconstruct temperature, precipitation, and atmospheric dust levels, and to provide records of changes in the strength of the Asian monsoon and El Nino-Southern Oscillation ([1][1]). As shown in the figure, the total area of the summit glacier on Mt. Kilimanjaro decreased by 82% between 1912 and 2000. Soon, the only information left from the Kilimanjaro ice will be what is contained in the cores extracted last year and stored in freezers at Ohio State University. The situation on Kilimanjaro is not unique. Tropical warming is causing the rapid retreat of ice caps and glaciers at high elevations in the tropics and subtropics around the world ([2][2]). A second example of paleoarchives that are being lost is the widespread damage to tropical corals. Measurements in corals have been successfully used to reconstruct sea surface temperature, salinity, and the surface circulation of the tropical oceans for the past several hundred years, and for isolated windows in the more distant past ([3][3]). Large living corals (more than 100 to 200 years old) suitable for climate reconstruction purposes are relatively rare in most reef areas of the world. These corals are under intense pressure from a myriad of localized stresses related to coastal development and population pressure. In addition, widespread bleaching and mortality of corals are occurring with increasing frequency as the consequences of rising temperatures. Furthermore, studies indicate that corals and other calcifying marine organisms are subject to geochemical stresses from rising CO2 concentrations in seawater ([4][4]). Another biological source of paleoclimate records are tree rings, which have the potential to yield information on many aspects of tropical climate, from the Asian monsoon and El Nino to the factors controlling the storage of carbon in tropical forests ([5][5]). The use of tree rings from tropical trees is relatively new, but is moving into the phase where continental-scale collections must be made and analyzed. Massive felling of the commercially valuable timber of old-growth timber such as teak raises the possibility that, by the time scientists are able to sample them, many of the old trees containing the most valuable information will already have been sent to the sawmills. Paleoarchives provide a wealth of information about past variability of the climate system relevant to future concerns. Thus, we call for an internationally coordinated effort designed to rescue endangered natural archives of past environmental variability and initiate large-scale observational and experimental campaigns to investigate the processes recorded in these natural archives. 1. [↵][6]1. L. G. Thompson , Quat. Sci. Rev. 19, 19 (2000). [OpenUrl][7][CrossRef][8] 2. [↵][9]An overview of the status of glaciers around the world is available from the world glacier monitoring service at . 3. [↵][10]1. M. K. Gagan 2. et al. , Quat. Sci. Rev. 19, 45 (2000). [OpenUrl][11][CrossRef][12] 4. [↵][13]An overview of regions susceptible to bleaching can be found at: . 5. [↵][14]1. R. D'Arrigo , PAGES News 6, 14 (1998). [OpenUrl][15] [1]: #ref-1 [2]: #ref-2 [3]: #ref-3 [4]: #ref-4 [5]: #ref-5 [6]: #xref-ref-1-1 View reference 1 in text [7]: {openurl}?query=rft.jtitle%253DQuat.%2BSci.%2BRev.%26rft.volume%253D19%26rft.spage%253D19%26rft.atitle%253DQUAT%2BSCI%2BREV%26rft_id%253Dinfo%253Adoi%252F10.1016%252FS0277-3791%252899%252900052-9%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [8]: /lookup/external-ref?access_num=10.1016/S0277-3791(99)00052-9&link_type=DOI [9]: #xref-ref-2-1 View reference 2 in text [10]: #xref-ref-3-1 View reference 3 in text [11]: {openurl}?query=rft.jtitle%253DQuat.%2BSci.%2BRev.%26rft.volume%253D19%26rft.spage%253D45%26rft.atitle%253DQUAT%2BSCI%2BREV%26rft_id%253Dinfo%253Adoi%252F10.1016%252FS0277-3791%252899%252900054-2%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [12]: /lookup/external-ref?access_num=10.1016/S0277-3791(99)00054-2&link_type=DOI [13]: #xref-ref-4-1 View reference 4 in text [14]: #xref-ref-5-1 View reference 5 in text [15]: {openurl}?query=rft.jtitle%253DPAGES%2BNews%26rft.volume%253D6%26rft.spage%253D14%26rft.atitle%253DPAGES%2BNEWS%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx

Coring at site ODP 1033B in Saanich Inlet recovered 59.4 m of mainly laminated olive-grey diatom ooze and an underlying 55.15 m of massive grey to olive-grey silty clay. Based on AMS radiocarbon dating, the boundary between the two units is between 11,000 and 13,800 calibrated years BP, and represents the Holocene-Pleistocene boundary. The lower unit represents glaciomarine deposition, whereas deposition of the upper unit began when the modern semi-restricted physiography of the fjord was established following glacial rebound and highly productive marine conditions were established. The glaciomarine clay is almost entirely terrigenous, whereas the diatom ooze contains 2–3 wt.% organic C and 20–40 wt.% biogenous silica; CaCO3 contributions are minor, but there are several peaks in carbonate abundance in the upper unit. The isotopic composition of organic C and total N suggests that organic matter in the glaciomarine clay is dominantly terrestrial (δ13Corganic<−25‰ and δ15Ntotal=ca. 3‰) and in the diatom oozes it is mainly marine (δ13Corganic>−22‰ and δ15Ntotal=ca. 10‰). The heavy δ15Ntotal values probably record a contribution of isotopically heavy nitrate to the surface waters of the inlet that is transported to British Columbia (BC) coastal waters from the eastern tropical Pacific by the California Undercurrent. Major and minor elemental data suggest that the composition of the terrigenous material and its grain-size has changed over the last 15 kyr, and there are marked enrichments in several redox-sensitive elements in the diatom oozes. Thus, Cu, Mn, Mo, Ni, Pb, V and Zn have higher concentrations in the upper unit; Br and I are also enriched because of their association with organic matter. Mn is enriched in the anoxic diatom oozes due to the presence of manganoan carbonate (Mn peaks generally corresponding with carbonate peaks) formed in the sediment when deep water renewal caused precipitation of Mn oxyhydroxides, which dissolved in the anoxic sediment and was precipitated as a diagenetic phase. The remaining metals are enriched because of their removal to the sediment as sulphides (Cu, Mo, Ni, Pb and Zn) or as particle-reactive reduced species (V). Cr enrichment is obscured by the presence of Fe-rich chlorite. The lag in the enrichment of Mo with respect to organic C in the sediments indicates that anoxia developed some time after marine production increased following the semi-isolation of the fjord.

Changes in palaeoproduction in Saanich Inlet, British Columbia, were examined from sediments using total organic carbon contents and stable carbon isotope ratios. Sediments were obtained from Holes 1033B and 1034B of Ocean Drilling Program Leg 169S. These cores contain two distinct zones: (1) carbon poor (%Corg<0.5wt.%) glaciomarine muds from the upper Pleistocene, and (2) carbon rich (%Corg1–3wt.%), well-laminated sediments from the Holocene. A slight monotonic rise in %Corg and δ13Corg throughout the Holocene suggests that primary production in the inlet has been steadily increasing. Some influence of changes in local land vegetation is also evident. Sharp decreases in %Corg and δ13Corg in the early Holocene probably represent material deposited from a major flood. Differences in organic δ13Corg between light and dark laminae are related to seasonal variations in species composition temperature and nutrient conditions.

Motivated by the rapid increase in atmospheric CO2 due to human activities since the Industrial Revolution, several international scientific research programs have analyzed the role of individual components of the Earth system in the global carbon cycle. Our knowledge of the carbon cycle within the oceans, terrestrial ecosystems, and the atmosphere is sufficiently extensive to permit us to conclude that although natural processes can potentially slow the rate of increase in atmospheric CO2, there is no natural "savior" waiting to assimilate all the anthropogenically produced CO2 in the coming century. Our knowledge is insufficient to describe the interactions between the components of the Earth system and the relationship between the carbon cycle and other biogeochemical and climatological processes. Overcoming this limitation requires a systems approach.