Changes in the terrestrial environment and their effect on marine carbonates

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Increased terrestrial runoff associated with coastal development results in fine particles suspended in shallow marine waters, which clogs pores in coral skeletons and reduces the amount of sunlight reaching the reefs. Excess nutrients associated with runoff are also harmful to reefs because they have negative impacts on the relationship between coral hosts and their photosynthetic symbionts. The immediate impacts of siltation and enhanced nutrients on reefs are fairly well understood; however, there are few studies examining the long-term effects of enhanced weathering or how carbonate producing biota in non-reef environments may be affected by these stressors. The overall objective of this research program is to evaluate the effects of terrestrial runoff and associated nutrients in various marine environments and through a range of timescales. This research proposal focuses on two main objectives that examine: 1) the effect the Earth's first forests and soils had on Devonian (Frasnian - 380 Ma) reefs; and 2) the effects of runoff in modern non-reef environments. The Frasnian expansion of forests and development of root networks, known as the punctata Event (pE), resulted in the world's first soils. It is assumed that this event had an effect on carbonate producing biota in the world's oceans since modern reefs suffer from increased soil runoff; however, the effects of this event on Frasnian reefs has not been explored. The proposed research examines the impact of the pE on ancient reefs that are well-preserved in the Western Canadian Sedimentary Basin. The research will also entail correlation of biogenically-sourced silicas in marine shales, which may represent ancient phytoplankton blooms, coeval with the pE, and responsible for enhanced bottom water anoxia observed worldwide at this time. The second aspect of this research proposal investigates the impact of terrestrial runoff, associated nutrients, and heavy metals on carbonate-producing biota in two modern settings: a lagoon in Grand Cayman and across an inner carbonate ramp in Abu Dhabi. The recent sedimentary record (<1000 years) will be interrogated for foraminifera and sediment geochemistry. Foraminifera are sensitive to changes in nutrient levels where, comparable to corals, larger symbiont-bearing foraminifera are replaced by generalist taxa. These generalist taxa also positively correlate with metals in sediments. The ultimate goal of this research is to determine how increased runoff along developed coastlines has impacted carbonate-producing marine biota in non-reef environments and develop criteria that may help us to recognize the effects of nutrification in ancient environments.