Extracting Past Climate and Local Sea Level Change from the Geologic Record of Coastal Sediment Transport in The Bahamas
Abstract
Detailed reconstructions of past interglacial Earth climate provide a baseline to differentiate natural variability from human caused change and can reveal feedbacks that may become fundamental in predicting future climate change. In the last interglacial period (marine isotope stage 5e; MIS 5e - 128 to 116 kyr BP), global mean sea level was up to 6-9 meters higher than today, and greenhouse gases were similar to pre-industrial levels. If these observations are valid, they suggest that current sea level may be primed for sudden and drastic change. However, the exact elevation of global sea level during MIS 5e, and the rates of change during that interglacial are complicated by incomplete chronologies in the geologic record and uncertainties in local isostatic or tectonic adjustment of these records since deposition. The Bahamian archipelago consists of several isolated, shallow carbonate platforms that are tectonically stable and may record a relatively straightforward history of past interglacial sea level. The rocky islands on the eastern margins of the platforms are composed of carbonate sediments arranged in coast-parallel and V-shaped coast-perpendicular ridges as high as 20-30 meters above modern sea level. There is a lack of scientific consensus as to whether these sediments were deposited by the ocean during an interval of higher sea level (MIS 5e or 11), or if the ridges are aeolian carbonate dunes. We scan hand samples from these deposits and develop image segmentation code to isolate individual grains. With this dataset, we quantify the relative arrangement of grain sizes and shapes to objectively identify evidence of aeolian depositional features such as the inverse grading of ripple sets. Additionally, the modern average wind direction in the Bahamas aligns with the observed orientation of V-shaped ridges across the archipelago within 10 degrees. Remarkably, there are very few active dunes in the Bahamas today, which raises an important discussion on the timing of deposition and the role that the geologic record of aeolian carbonates may have in inferring past climate and local sea level dynamics.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFMPP51B2310D
- Keywords:
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- 0726 Ice sheets;
- CRYOSPHEREDE: 1621 Cryospheric change;
- GLOBAL CHANGEDE: 1641 Sea level change;
- GLOBAL CHANGE