U/Th‐dated sclerosponges from the Indonesian Seaway record subsurface adjustments to west Pacific Winds

Abstract

Abstract. Stable isotope records from sclerosponges collected at 10-20 m depth in the Indonesian Seaway and Solomon Islands are particularly well suited for reconstructing century-scale trends in ambient temperature variability and the oceanic uptake of fossil fuel carbon. Basal U/Th dates demonstrate that the sclerosponges analyzed are 85-100 years old. Isotopic records from the Indonesian specimens suggest a strong subsurface cooling over the past 20 years that is not manifested in either surface instrumental or shallower coral proxy records. However, analysis of observed subsurface temperatures in Indonesia, observed winds in the west Pacific, and simulated subsurface temperatures from a steady state general circulation model hindcast forced by observed winds combine to suggest that thermocline adjustments could account for at least part of the recent cooling inferred from the Indonesian sclerosponges. If so, the sclerosponge data suggests that, on average, the west Pacific thermocline has shoaled significantly over at least the past 2 decades.

Intra‐annual variation in the stable oxygen and carbon and trace element composition of sclerosponges

“…Nevertheless, several workers have shown that sclerosponges can be successfully dated using a variety of methods and contain proxy records of their environment which can be interpreted to yield climatic and environmental information. These studies have used a range of sampling resolutions, from a fairly coarse sampling interval [ Druffel and Benavides , 1986; Benavides and Druffel , 1986], to progressively finer sampling [ Böhm et al , 1996, 2000; Moore et al , 2000]. The latest studies of Fallon et al [1999] and Lazareth et al [2000] have employed a laser microprobe coupled to an ICP‐MS, allowing them to sample at resolutions approaching 20 μm.…”

Constraining initial 230Th activity in incrementally deposited, biogenic aragonite from the Bahamas

“…It has been used with success on C. nicholsoni from the central Caribbean near the island of Jamaica (Bö hm et al, 2000;Haase-Schramm et al, 2003) and in the Bahamas (Swart et al, 2002;Rosenheim et al, 2005a,b). Growth rate has been shown to vary about the mean inter-annually (Swart et al, 2002), but over the life of an individual sclerosponge a constant growth rate assumption has been successful in chronicling anthropogenic geochemical trends Bö hm et al, 1996;Swart et al, 1998aSwart et al, ,b, 2002Lazareth et al, 2000;Moore et al, 2000;Haase-Schramm et al, 2003).…”

“…Established growth rates of 200 lm y À1 from these methods indicate that the concentric banding (formed at millimeter-scale increments) is not annual in nature. Because sclerosponge species C. nicholsoni incorporates three to five times the concentration of uranium (Swart et al, 1998a,b;Bö hm et al, 2000;Moore et al, 2000;Haase-Schramm et al, 2003) into its basal aragonite skeleton than do corals (Swart, 1979;Min et al, 1995;Shen and Dunbar, 1995;Cardinal et al, 2001), the 230 Th dating method has become the dating tool of choice for sclerosponge dating in paleoceanographic studies. It has been used with success on C. nicholsoni from the central Caribbean near the island of Jamaica (Bö hm et al, 2000;Haase-Schramm et al, 2003) and in the Bahamas (Swart et al, 2002;Rosenheim et al, 2005a,b).…”

“…An assumption of zero [ 230 Th/ 232 Th] i has been made in several projects involving the U/Th dating of young marine carbonates (Barnes et al, 1956;Edwards et al, 1986;Bö hm et al, 1996Bö hm et al, , 2000Moore et al, 2000;Swart et al, 2002;Haase-Schramm et al, 2003). In such cases, when initial activities of thorium are assumed negligible, the 230 where d 234 U m is the oceanic secular disequilibrium which is measured for each sample, but in the vicinity of 146 ± 10‰ (Bard et al, 1991;Stirling et al, 1998;Cheng et al, 2000b;Henderson, 2002;Robinson et al, 2006).…”

Anthropogenic and solar forcing in δ13C time pattern of coralline sponges

“…Böhm et al [4] analyzed the carbon isotope records of the sponge Ceratoporella nicholsoni in samples collected from the Caribbean Sea (Jamaica). These sponges precipitate aragonite very close to isotopic equilibrium with ambient sea water [5][6][7], so they provide an excellent proxy both for the anthropogenic carbon isotope shift of the nineteenth and twentieth centuries [5,6,[8][9][10][11] and for the preindustrial variations. On the basis of ice core analyses, Etheridge et al [12] evidenced a 6 ppm change in the atmospheric CO 2 partial pressure (pCO 2 ) before the onset of industrial influences, accompanied by simultaneous variations in carbon isotope data of ice core inclusions [13].…”