Bermuda isotopic composition

Knapp, A. N., Sigman, D. M., and Lipschultz, F. (2005). N isotopic composition of dissolved organic nitrogen and nitrate at the Bermuda Atlantic time-series study site. Global Biogeochemical Cycles 19(1), GB1018. 

Turekian V. C., Macko S. A., and Keene W. C. (2003) Concentrations, isotopic compositions, and sources of size-resolved, particulate organic carbon and oxalate in nearsurface marine air at Bermuda during spring. J. Geophys. Res. 108, 4157, doi 10.1029/2002JD002053. 

The diversity in stable carbon isotopic compositions evident at the molecular level became apparent with the advent of gas chromatography coupled to isotope ratio mass spectrometry (IRM-GC-MS e.g., Hayes et al., 1990). More recently, age variations among different biomarkers have been investigated (e.g., Eglinton et al., 1997 Pearson et al., 2001). Substantial variability has been observed where inputs from diverse sources are encountered, even within depth horizons representing short periods of sediment accumulation. For example, surficial sediments from the Bermuda Rise in the northern Sargasso Sea deposited over a time span of less than 300 yr... 

Figure 4 Mg/Ca of different planktonic foraminifera from a Bermuda sediment trap time series, plotted versus calcification temperatures calculated from the oxygen isotopic composition of the shells (Anand et aL, 2003) (reproduced by permission of American Geophysical Union from Paleoceanography 2003, 18, 1050). The aggregate fit to all the data in the plot is Mg/Ca = 0.38 exp(0.09T), very similar to relationships derived from culturing and core-top studies.

In some cases, such as Bermuda and central Texas (Harmon, 1975), there is a distinct bias toward either winter or summer rainfall. In other instances, particularly in semi-arid areas of strongly seasonal precipitation like Israel (Bar-Matthews et al., 1996 Ayalon et al., 1998) and New Mexico (Chapman et al., 1992), the isotopic composition of recharge waters can be substantially modified by evaporation and mixing processes within the epikarst zone. 

---