This research centers on the extraction of environmental information stored in the calcium carbonate skeletons of corals (Porites) and coralline sponges (Astrosclera willeyana). Elemental variations are measured in these samples using laser ablation inductively coupled plasma mass spectrometry. During this project, techniques were refined and developed to quantitatively measure major (B, Mg, Sr, Ba, U) and minor (Mn, Zn, Pb, REE’s) elemental abundances in corals and coralline sponges.

Cores from Porites sp. coral colonies were collected from inshore, mid-shelf and outer reef localities (central Great Barrier Reef) to test the robustness of the major elemental SST and runoff proxies (B/Ca, Mg/Ca, Sr/Ca, Ba/Ca, U/Ca). The inshore reefs selected for this study are heavily influenced by river runoff whereas the mid-reef and outer-reef locations are not. It is shown that Ba/Ca provides an excellent proxy for river runoff. Time series analyses of Sr/Ca, U/Ca, B/Ca and Mg/Ca are compared to in situ sea surface temperature (SST) and/or IGOSS NMC weekly satellite SST to provide calibrations for these elements. Both the U/Ca and Mg/Ca have calibrations within error for mid-shelf and outer reef corals but the calibrations differ for the inshore corals. Sr/Ca and B/Ca appear to be the most robust of the elemental temperature proxies in terms of recording water temperature. Measurements of coral manganese suggest a seasonal cycle closely linked to solar radiation and wind. Increased solar radiation may increase the dissolved seawater Mn that result in corals having elevated concentrations of Mn during the summer.

The use of corals as recorders of marine pollution was examined on the island of Misima in Papua New Guinea where open-cut gold mining commenced in 1989. This mining caused increased sedimentation affecting the nearby fringing coral reef to varying degrees, causing coral mortality (complete suffocation) in some areas. Eight coral colonies (2 from high sedimentation, 2 transitional, 2 minor and 2 unaffected control sites) were analyzed for Mn, Y, La, Ce, Zn and Pb. All sites show low steady “background” levels prior to the commencement of mining. After mine construction began in 1988, all sites aside from the control show dramatic increases of Mn, Y, La, and Ce associated with the increased sedimentation. Zn and Pb increase after 1989 when ore processing began. The concentration of these elements in these corals decreases as the distance from the mine increases. Rare earth elements (REE) measured in two corals suggest a pattern different from “normal” seawater. When the coral REE pattern is compared to seawater an enrichment of the light and middle REE’s appear. The heavy REE’s are depleted relative to the seawater pattern. This suggests the nearshore seawater REE’s are influenced by island weathering.

Coralline sponges have been proposed as a new source of tropical paleoclimatic information. Profiles of d13C in coralline sponges have documented (better and more accurately than corals) the atmospheric increase of 12C associated with increased fossil fuel consumption. Due to their very slow growth rates ~0.2 mm/yr sponges are better suited to recording and providing long-term environmental information rather than annual information. These sponges appear to smooth the record stored in their skeleton by adding secondary aragonite near the base of the living tissue layer. This smoothing limits their use as annual environmental recorders but still enables their use for decadal or longer environmental fluctuations. Smoothed records of Sr/Ca from five sponges around the Southwest Pacific suggest that these sponges are able to capture 5 yr. and longer seawater temperature anomalies over the past 50-200 years.
email: fallon4@llnl.gov