Ocean proxies

Henderson GM (2002b) New oceanic proxies for paleoclimate. Earth Planet Sci Lett 203 1-13 Henderson GM, Burton KW (1999) Using ( " U/ U) to assess diffusion rates of isotopic tracers in Mn cmsts. Earth Planet Sci Lett 170(3) 169-179... 

Henderson, G. M. New oceanic proxies for paleoclimate. Earth Planet. Sci. Lett. 2002,203, 1-13. 

A major opportunity to test the use of " Th as a proxy for POC flux arose with the Joint Global Ocean Flux Study (JGOFS). JGOFS had as a central goal a better understanding of the ocean carbon cycle, including the flux of POC leaving the euphotic zone. Process studies were carried out in the Atlantic Ocean, Pacific Ocean, Arabian Sea and Southern Ocean. " Th profiles were obtained as a part of each process study. 

The role of advection also was shown clearly by Friedrich and Rutgers van der Loeff (2002) in the Southern Ocean, especially when attempting to use °Po as a proxy for the estimation of POC and biogenic silica export. These authors pointed out that the °Pb pair could be used to constrain POC and biogenic silica export fluxes if advection could be properly characterized. 

Walter HJ, Rutgers van der Loeff MM, Hoeltzen H (1997) Etrhanced scavenging of Pa relative to h in the South Atlantic south of the Polar front Implicatiotts for the use of the Pa/ h ratio as a paleoproductivity proxy. Earth Planet Sci Lett 149 85-100 Wheatcroft RA (1992) Experimental tests for particle size-dependant biotirrbidation in the deep oceans. Linmol Oceanogr 37(1) 90-104... 

Residence time and reactivity are strongly correlated through equation (7.2.9). This is true for seawater composition since Whitfield and Turner (1979) showed a rather good correlation between oceanic residence times and seawater-crustal rock partition coefficients which are taken as a measure of element reactivity in the ocean. Actually, a better estimate of reactivity is given by oceanic suspensions, so Li (1982) suggested to use pelagic clay-seawater concentration ratios as a proxy to partition coefficients. 

Measurements of radionuclides in seawater have been used to study a variety of processes, including ocean mixing, cycling of materials, and carbon flux (by proxy). These measurements provide information on both process rates and mechanisms. Because of the unique and well-understood source functions of these elements, models of radionuclide behavior have often led to new understanding of the behavior of other chemically similar elements in the ocean. 

Druffel, E. R.M. 1995. Geochemistry of corals Proxies of past ocean chemistry, ocean circulation and climate. National Academy of Sciences Colloquium on Carbon Dioxide and Climate Change. 

Finally, because the Mo ocean budget should be strongly sensitive to bottom water redox conditions, particularly perturbations associated with expanded deep sea anoxia, determination of Mo concentrations or their variations in ancient seawater, via sedimentary proxies, has been proposed as an indicator of global ocean paleoredox change (e.g., Emerson and Huested 1991). 

Due to the preferential extraction of Mo from ocean water, the ocean is the heaviest Mo reservoir of all sources analyzed so far Fig. 2.24, consequently the Mo isotope composition of the ocean is sensitive to redox changes and thus can be nsed as a paleo-redox proxy. 

Black shales that are formed in an anoxic environment such as the Black Sea have a Mo isotope composition nearly identical to ocean water (Barling et al. 2001 Arnold et al. 2004 Nagler et al. 2005). Organic carbon rich sediments formed in suboxic environments have variable Mo/ Mo ratios intermediate between those of ocean water and oxic sediments (Siebert et al. 2003). Thus Mo isotope values in ancient black shales can be used as a paleo-oceanographic proxy of the oxidation state of the ocean, as for example has been discussed by Arnold et al. (2004) for the Proterozoic. Figure 2.25 summarizes natural Mo isotope variations. 

Quasi A, Hoefs J, Paul J (2006) Pedogenic carbonates as a proxy for palaeo-C02 in the Paleozoic atmosphere. Palaeogeogr Palaeochmatol Palaeoecol 242 110-125 Quay PD, TUbrook B, Wong CS (1992) Oceanic uptake of fossil fuel CO2 carbon-13 evidence. Science 256 74-79... 

Buesseler KO, Benitez-Nelson CR, Moran SB, Burd A, Charette M, Cochran JK, Coppola L, Fisher NS, Fowler SW, Gardner WD, Guo LD, Gustafsson O, Lamborg C, Masque P, Miquel JC, Passow U, Santschi PH, Savoye N, Stewart G, Trull T (2006) An assessment of particulate organic carbon to thorium-234 ratios in the ocean and their impact on the application of 234Th as a POC flux proxy. Mar Chem 100 213-233... 

Schneider, R. R., P. J. Muller, and M. Zabel. 1996. "Biogenic opal in the eastern South Atlantic patterns of surface water productivity, sedimentary accumulation, and benthic silicate fluxes in relation to oceanic and fluvial nutrient supply." In OPALEO On the Use of Opal as a PaleoProductivity Proxy, ed. O. Ragueneau, A. Leynaert, and P. Treguer (Brest, France), pp. 98-103. 

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