『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 (PO4SW) concentration.
Further, high-resolution P/Ca records in multiple colonies of
Pavona gigantea and Porites lobata corals grown
at the same upwelling locations in the Gulf of Panama(最後のaの頭に´)
were strongly correlated to a contemporaneous time-series record
of surface water PO4SW
at this site (r2 = 03.7-0.9). This study supports application
of the following multi-colony calibration equations to down-core
records from comparable upwelling sites, resulting in ±0.2 and
±0.1μmol/kg uncertainties in PO4SW
reconstructions from P. lobata and P. gigantea,
respectively.
P./CaPorites lobata (μmol/mol) =
(21.1±2.4) PO4SW (μmol/kg)
+ (14.3±3.8)
P./CaPavona gigantea (μmol/mol) =
(29.2±1.4) PO4SW (μmol/kg)
+ (33.4±2.7)
Inter-colony agreement in P/Ca response to PO4SW 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.』
1. Introduction
2. Methods
2.1. Samples
2.1.1. Global P/Ca distribution
2.1.2. Local calibrations
2.2. Analyses
2.2.1. Sample preparation
2.2.2. Statistical analysis
3. Results and discussion
3.1. Global P/Ca distribution
3.2. Multi-colony P/Ca calibration with in situ PO4SW concentration
3.2.1. Age model
3.2.2. Inter-colony calibration reproducibility
3.2.3. Inter-genus agreement
3.3. Global distribution versus local calibration
3.4. Other potential influences on P/Ca
3.4.1. Extension rate
3.4.2. Temperature
3.4.3. Additional forms of seawater phosphorus
4. Conclusions
Acknowledgments
Appendix A. Supplementary data
References