Abstract:
In the Drake Passage, between Antarctica and South America, bioturbation increases during warmer (open ocean) intervals during Marine Isotope 31. Marine Isotope 31 is a period of time approximately 1 million years ago that is considered an analog to the modern day Antarctic climate because it is the most recent geological warm period and had temperatures similar to current Antarctic temperatures. Analyzing the abundance of bioturbation during MIS 31 allows us to understand and predict how Antarctic ecosystems will react to warming temperatures.
One way of understanding oceanic ecosystems’ reactivity to temperature changes can be done through observing the abundance and types of bioturbation presented in split cores. Bioturbation is the modification animals and plants make to soil. Examples of bioturbation are traces like footprints or burrows. The main focus of this project is looking at bioturbation abundance (area percentage) on split core surfaces that correspond to warm and cool periods in MIS 31. Being able to determine warm and cool periods within this data is based on the presence and types of surface dwelling diatoms. Fragilariopsis kerguelensis is an open ocean diatom, meaning that an increase in the presence of it signals that there was less ice and more open water and warmer temperatures. Less of it means there was less open water, more ice and cooler temperatures. The abundance of F. Kerguelensis alternates at about a twenty thousand year periodicity between warm and cool periods (Warnock et al., in review). In addition to temperature, diatom abundance is also an indicator of productivity; higher productivity during warmer times and lower productivity during cooler times.
Using sediment cores from IODP expedition 382, site 1537 in the Dove Basin (Drake Passage), images of the cores were obtained. The images selected corresponded to periods of high and low productivity (based on F. Kerguelensis abundance) in MIS 31. Once the images were obtained, they were analyzed in Adobe Photoshop to enhance the visibility of bioturbation. After the bioturbation became more visible, the percent bioturbation that made up the image was determined by counting the pixels of the bioturbated area in the modified core images. This allowed for the comparison of bioturbation percentages in warmer and cooler intervals. The analysis concludes that during open ocean times, which are assumed to be warmer and have high primary productivity, there is more bioturbation and in cooler times with more sea ice cover and lower productivity there is less bioturbation.
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