Thanks!
Here's a nice table with references. I think that 8 ppm is the currently accepted value.
http://users.rcn.com/patwilde/ocpertbl.html
I don't have any especially recent references with the actual measured values for me to post, but I'm sure that they are in these articles if you want to look them up:
Seawater strontium and Sr/Ca variability in the Atlantic and Pacific oceans. de Villiers, S. Department of Geological Sciences, University of Washington, Seattle, WA, USA. Earth and Planetary Science Letters (1999), 171(4), 623-634.
Abstract
Seawater Sr and Sr/Ca exhibit spatial gradients 2-3% globally; the deep ocean is more enriched relative to the surface. In latitudinal transects, highest surface values were obsd. at high latitudes and were assocd. with areas of upwelling. A pronounced upper ocean vertical Sr gradient was attributable to the prodn. of celestite skeletons by surface-dwelling Acantharia, coupled to a shallow dissoln. cycle. The upper ocean residence time of Sr with respect to celestite cycling is much shorter than its global oceanic residence time. Although the magnitude of seawater Sr/Ca variability is relatively small, it is significant with respect to high-precision paleoceanog. applications. Sr/Ca gradients in the contemporary ocean also complicates evaluating Quaternary changes in seawater Sr/Ca which may have resulted from other processes, such as aragonite recrystn. during sea-level low stands.
A Cenozoic seawater Sr/Ca record from benthic foraminiferal calcite and its application in determining global weathering fluxes. Lear, C. H.; Elderfield, H.; Wilson, P. A. Institute of Marine and Coastal Sciences, Rutgers University, New Brunswick, NJ, USA. Earth and Planetary Science Letters (2003), 208(1-2), 69-84.
Abstract
A Cenozoic multi-species record of benthic foraminiferal calcite Sr/Ca has been produced and is cor. for inter-specific offsets (typically less than 0.3 mmol/mol) and for the linear relationship between decreasing benthic foraminiferal Sr/Ca and increasing water depth. The water depth correction, detd. from Holocene, Late Glacial Maximum and Eocene paleowater-depth transects, is .apprx.0.1 mmol/mol/km. The cor. Cenozoic benthic foraminiferal Sr/Ca record ranges from 1.2 to 2.0 mmol/mol, and has been interpreted in terms of long-term changes in seawater Sr/Ca, enabling issues related to higher-resoln. variability in Sr/Ca to be ignored. We est. that seawater Sr/Ca was .apprx.1.5 times modern values in the late Cretaceous, but declined rapidly into the Paleogene. Following a min. in the Eocene, seawater Sr/Ca increased gradually through to the present day with a min. superimposed on this trend centered in the late Miocene. By assuming scenarios for changing seawater calcium concn., and using published carbonate accumulation rate data combined with suitable values for Sr partition coeffs. into carbonates, the seawater Sr/Ca record is used to est. global av. river Sr fluxes. These fluxes are used in conjunction with the seawater strontium isotope curve and ests. of hydrothermal activity/tectonic outgassing to calc. changes in global av. river 87Sr/86Sr through the Cenozoic. The abs. magnitude of Sr fluxes and isotopic compns. calcd. in this way are subject to relatively large uncertainties. Nevertheless, our results suggest that river Sr flux increased from 35 Ma to the present day (roughly two-fold) accompanied by an overall increase in 87Sr/86Sr (by .apprx.0 to 0.001). Between 75 and 35 Ma, river 87Sr/86Sr also increased (by .apprx.0.001 to 0.002) but was accompanied by a decrease (two- to three-fold) in river Sr flux.
An assessment of the Sr/Ca ratio in shallow water hermatypic corals as a proxy for sea surface temperature. Marshall, John F.; McCulloch, Malcolm T. Research School of Earth Sciences, Australian National University, Canberra, Australia. Geochimica et Cosmochimica Acta (2002), 66(18), 3263-3280.
Abstract
The high precision measurement of the Sr/Ca ratio in corals has the potential for measuring past sea surface temps. at very high accuracy. However, the veracity of the technique has been questioned on the basis that there is both a spatial and temporal variation in the Sr/Ca ratio of seawater, and that kinetic effects, such as the calcification rate, can affect the Sr/Ca ratio of corals, and produce inaccuracies of the order of 2-4 C. A no. of cores of the massive hermatypic scleractinian coral Porites, from the central Great Barrier Reef, have been analyzed for Sr/Ca at weekly to monthly resoln. Results from a 24 yr record from Myrmidon Reef show an overall variation from 22.7 C to 30.4 C. The record shows a warming/cooling trend with max. warming centered on the 1986-1987 summer. While some bleaching was reported to have occurred at Myrmidon Reef in 1982, the Sr/Ca record indicates that subsequent summer temps. were much higher. The 4.5 yr record from Stanley Reef shows a max. SST of 30 C during the 1997-1998 El Nin~o event. The calibrations from Myrmidon and Stanley Reefs are in excellent agreement with previously published calibrations from nearby reefs. While corals do not calcify in equil. with seawater due to physiol. control on the uptake of Sr and Ca into the lattice of coralline aragonite, it can be argued that, provided only a single genus such as Porites sp. is used, and that the coral is sampled along a major vertical growth axis, then the Sr/Ca ratio should vary uniformly with temp. Similarly, objections based on the spatial and temporal variability of the Sr/Ca activity ratio of seawater can be countered on the basis that in most areas where coral reefs grow there is a uniformity in the Sr/Ca activity ratio, and there does not appear to be a change in this ratio over the growth period of the coral. Evidence from several corals in this study suggest that stress can be a major cause of the breakdown in the Sr/Ca-SST relationship.
Thermal stress, resulting from either extremely warm or cool temps., can produce anomalously low Sr/Ca derived SSTs as a result of the breakdown of the biol. control on Sr/Ca fractionation. It is considered that other stresses, such as increased nutrients and changes in light intensity, can also lead to a breakdown in the Sr/Ca-SST relationship. Two of the main issues affecting the reliability of the Sr/Ca method are the calibration of the Sr/Ca ratio with measured SST and the estn. of tropical last glacial max. (LGM) palaeotemperatures. Instead of producing a const. calibration, just about every one published so far is different from the others. What is obvious is that for most calibrations while the slope of the calibration equation is similar, the intercepts are not. While the cause for this variation is still unknown, it would appear that corals from different localities around the world are responding to their own particular environment or that certain types of environments exert a control on the corals' physiol. Sr/Ca derived SST ests. for the LGM and deglaciation of 5-6 cooler than present are at odds with ests. of 2-3 cooling by other climate proxies. The apparent lack of reef growth during the LGM suggests that SSTs were too cold in many parts of the tropics for reefs to develop. This would lend support to the idea that tropical SSTs were much cooler than what the CLIMAP data suggests.
