A multi-proxy approach is utilized on mm- to cm-scale laminated sediment records in coastal salt ponds on St. John, U.S. Virgin Islands to characterize the sediments, identify their sources and depositional processes/events (heavy rainfall, tropical cyclones, tsunamis). Historical records are combined with high-resolution geochronology (short-lived radioisotopes, 210Pb, 137Cs, 7Be) and scanning elemental techniques (XRF and LA-ICP-MS) to link depositional events to how they are manifested in the sedimentary record. Volcanic rocks are the terrigenous sediment source and the sedimentary signature of terrigenous sediment in the geologic record consists of higher amounts of Al, Fe, Ti, Co, and Si, and is associated with terrigenous runoff due to rainfall events. A minimum threshold value of >2.0 mm per day (minimum to erode and transport terrigenous sediment downslope) of rainfall has been determined for the study area. The frequency of heavy rainfall events that exceed the threshold of >2.0 mm per day is significantly correlated to the amount of terrigenous sediment accumulation of the terrigenous indictor element Al measured by scanning LA-ICP-MS. There is a robust sedimentary record of terrigenous sediment runoff that is a function of the frequency of heavy rainfall events (exceed threshold). Variability in the sedimentary record reflects changes between periods of "wet" increased frequency of heavy rainfall events and "dry" decreased frequency of heavy rainfall events. Tropical cyclones and tsunamis can cause marine overwash into salt ponds leading to deposition of marine sediments. Elemental scans for Ca and Sr and overwash indicator elements are complicated by grain size effects of LA-ICP-MS techniques, as well the difficulty in differentiating between tropical cyclone overwash deposits and tsunami deposits. By defining the sedimentary signature for depositional events , geologic records can be interpreted to provide insight into the natural variability of these processes throughout geologic time for comparisons to the more recent anthropogenic time period. This study provides a framework that can be applied to other coastal environments on high-relief tropical islands, to compare local records, and provide information on regional processes controlling rainfall variability in tropical latitudes.

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[Truncated abstract. Formulae and special characters in this field can only be approximated. See PDF version for accurate reproduction.] Solar salt producers use solar energy to evaporate seawater as it flows through a series of ponds. The Shark Bay Salt solar ponds, at Useless Inlet in Western Australia, vary in salinity from that of seawater to four times seawater, over the pond sequence. Water column photosynthesis and biomass decreased markedly with increasing salinity along the pond sequence, while benthic productivity increased as cyanobacterial mats developed. Correspondingly, net productivity shifted from autotrophy to heterotrophy in the water column and from heterotrophy to autotrophy in the benthos. Both shifts occurred at intermediate salinity in the pond sequence, where there was low production in both the water column and benthos. Within individual ponds, productivity, algal biomass and physico-chemical conditions were relatively constant over the year of study. Transitions between benthic and planktonic production along the pond sequence were driven mostly by direct responses to salinity stress, as well as the formation of a gypsum crust on the pond floors at higher salinity (>120 g kg-1). This transition is similar to that which occurs in saline lakes undergoing anthropogenic salinisation and identifies critical salinities for the restoration of these lakes.