Coral skeleton P/Ca proxy for seawater phosphate: Multi-colony calibration with a contemporaneous seawater phosphate record

Abstract

A geochemical proxy for surface ocean nutrient concentrations recorded in coral skeleton could provide new insight into the connections between sub-seasonal to centennial scale nutrient dynamics, ocean physics, and primary production in the past. Previous work showed that coralline P/Ca, a novel seawater phosphate proxy, varies synchronously with annual upwelling-driven cycles in surface water phosphate concentration. However, paired contemporaneous seawater phosphate time-series data, needed for rigorous calibration of the new proxy, were lacking. Here we present further development of the P/Ca proxy in Porites lutea and Montastrea sp. corals, showing that skeletal P/Ca in colonies from geographically distinct oceanic nutrient regimes is a linear function of seawater phosphate (PO 4 SW ) concentration. Further, high-resolution P/Ca records in multiple colonies of Pavona gigantea and Porites lobata corals grown at the same upwelling location in the Gulf of Panamá were strongly correlated to a contemporaneous time-series record of surface water PO 4 SW at this site (r 2 = 0.7-0.9). This study supports application of the following multi-colony calibration equations to down-core records from comparable upwelling sites, resulting in ±0.2 and ±0.1 lmol/kg uncertainties in PO 4 SW reconstructions from P. lobata and P. gigantea, respectively. P=Ca Porites lobata ðlmol=molÞ ¼ ð21:1 AE 2:4ÞPO 4 SW ðlmol=kgÞ þ ð14:3 AE 3:8Þ P=Ca Pavona gigantea ðlmol=molÞ ¼ ð29:2 AE 1:4ÞPO 4 SW ðlmol=kgÞ þ ð33:4 AE 2:7ÞInter-colony agreement in P/Ca response to PO 4 SW was good (±5-12% about mean calibration slope), suggesting that species-specific calibration slopes can be applied to new coral P/Ca records to reconstruct past changes in surface ocean phosphate. However, offsets in the y-intercepts of calibration regressions among co-located individuals and taxa suggest that biologically-regulated "vital effects" and/or skeletal extension rate may also affect skeletal P incorporation. Quantification of the effect of skeletal extension rate on P/Ca could lead to corrected calibration equations and improved inter-colony P/ Ca agreement. Nevertheless, the efficacy of the P/Ca proxy is thus supported by both broad scale correlation to mean surface water phosphate and regional calibration against documented local seawater phosphate variations.

Acropora interbranch skeleton Sr/Ca ratios: Evaluation of a potential new high‐resolution paleothermometer

“…Following the release of the Fourth and Fifth Assessment Reports of the Intergovernmental Panel on Climate Change the scarcity of paleoclimate data representing tropical marine environments and the southern hemisphere has become increasingly clear [e.g., Intergovernmental Panel on Climate Change , ; Masson‐Delmotte et al , ]. Of the available high‐resolution paleoclimate records, coral colonies are particularly useful because skeletal geochemistry can provide subannual time series data on past water temperature [ Bagnato et al , ; DeLong et al , ; Epstein et al , ; Gagan et al , ; Grottoli and Eakin , ; McCrea , ], salinity [ Corrège , ; Felis et al , ; Gagan et al , ; Hendy et al , ; Le Bec et al , ; Pretet et al , ; Wu et al , ], pH [ Hemming and Hanson , ; Pelejero et al , ; Shinjo et al , ; Wei et al , ], and nutrient concentration [ LaVigne et al , , ]. On a global scale, such proxy data can help unravel Earth's natural climate variability and therefore improve computer model predictions of future climate.…”

Seawater nutrient and carbonate ion concentrations recorded as P/Ca, Ba/Ca, and U/Ca in the deep-sea coral Desmophyllum dianthus

“…In tropical corals these biogeochemical processes are explored using d 13 C, Ba/Ca (Lea et al, 1989;Tudhope et al, 1996;Alibert and Kinsley, 2008), and Cd/Ca and P/ Ca (Shen et al, 1987;LaVigne et al, 2010). A P/Ca proxy calibration was previously proposed for D. dianthus (Montagna et al, 2006), suggesting that P/Ca in the skeleton is $7 times greater than P/Ca in ambient seawater.…”

Systematic ENSO‐driven nutrient variability recorded by central equatorial Pacific corals

“…This broad‐scale reduction in nutrients is replicated in the Fanning and Christmas Island coral records as 37 ± 6% and 37 ± 8% decreases in P/Ca in June–August 1997 relative to mean P/Ca over 1 year prior to the El Niño event, respectively (Figures and ). The 6–8% uncertainty on the P/Ca reduction calculated using within‐run precision of P/Ca measurements (5–6%) is within the intercolony uncertainty found previously for Porites corals (5–12%) [ LaVigne et al ., ]. The trends in these two coral records are highly correlated (r = 0.82; 1997.4–1999.8), and the P/Ca dips correspond to the timing of the ~3°C warming during the 1997–1998 warm phase (Figure ).…”