When thinking about the Arctic, the picture that often comes to mind is an ice-covered ocean that grows and shrinks seasonally. In the Arctic region, the majority of the ice is sea ice, meaning that it floats directly on the seawater. Sea ice is less stable than land ice, resulting in the Arctic being very sensitive to climatic changes. To better anticipate future changes in this region, it is essential to improve understanding of how the Arctic has responded to climate change in the past. Currently available research can provide an estimate of historical sea ice extent that is instructive for both its description of past change, but also from a methodological standpoint by providing a robust, rigorous use of multiple proxies for past change. To understand how information like this might be used by decision makers, we contacted Dr. Whit Saumweber at the Center for Ocean Solutions, who noted that “improving public understanding of how these proxies are developed, and the rigor with which they are applied can help to increase public confidence in our understanding of climate impacts.” Our class discussed a 2010 paper by Leonid Polyak and colleagues, which describes a suite of evidence scientists use to determine when and where ice was present. Sediment cores drilled from the floor of the Arctic Ocean can be very illuminating, especially for capturing the oldest records of Arctic ice (50 million years ago). The size of sand, silt, and mud preserved on the ocean floor, as well as the type and chemistry of fossils, give researchers some indication of whether ice was covering the ocean at a particular time. However, modern sea ice cover makes these records difficult to obtain. Therefore, scientists often use more readily available lines of evidence that can be found in coastal areas around the Arctic, including the presence of driftwood and whalebones. Driftwood deposited during the past will only appear on ice-free coasts close to the edges of Arctic sea ice. The presence of wood (age dated using radiocarbon) on a coast indicates that Arctic ice extended to that point at the time the driftwood was deposited. Similarly, locations of ancient whalebones provides information on the extent of past ice as bowhead whales live near the margins of Arctic sea ice, but cannot cross large expanses of sea ice. During time periods in the past that Pacific and Atlantic bowheads were found together, scientists know the Arctic was ice-free at least for part of the summer, otherwise these animals would not have been able to cross the Arctic to coexist. Each piece of evidence only gives a portion of the record, but when combined they can tell us about the history of Arctic sea ice. Together, chemical and biological indicators in the sediment record (including sediments and microfossils) provide evidence for less Arctic sea ice at the beginning of the Holocene Epoch (~10,000 years ago). This conclusion is further supported by the scarcity of driftwood during this time, as well as the intermingling of Pacific and Atlantic bowhead whale bones. The full range of evidence shows progressive growth of sea ice through much of the Holocene (past 10,000 years), which is consistent with known cooling caused by an overall decrease in solar intensity. One exciting aspect of this paper is that it blends together many different lines of evidence to build a picture of past sea ice variability that is quite rigorously supported. About this research, Dr. Whit Saumweber added that “research such as that conducted by Polyak et. al. is incredibly useful for helping us contextualize both the scope and rate of change that the Arctic is facing. Their record historical sea ice extent forces us to recognize the unprecedented nature of this change and is helping to marshal an appropriate scale of international response to the climate crisis. In addition, many of the proxies they used to develop the sea ice record can themselves be useful for understanding ecosystem response to the radical change we are facing. This information in turn can be used to help communities that rely on these ecosystems prepare and adapt.” Along these lines, there are close linkages between changes in Arctic sea ice cover and ecosystems, specifically via types of marine species have been able to live in the Arctic or use it as a conduit to pass between the Pacific and Atlantic Oceans (e.g., Renaud et al., 2015). The paper by Renaud and colleagues documents that the Bering Strait opened between North America and Eurasia between 3 and 4 million years ago (m.y.a) during a period of increased temperature and sea ice melting called the mid-Pliocene warm period. This event allowed taxa from the North Pacific to expand into the Arctic and the Atlantic Ocean, and vice versa. After the opening of the Bering Strait and subsequent animal migrations, the global climate cooled significantly approximately 3 m.y.a. and initiated the formation of the Arctic ice sheet. Colder temperatures and presence of sea ice caused geographic isolation between the Pacific and Atlantic oceans and only animals that were able to adapt to extreme cold conditions could survive in the Arctic itself. The geologic record of ice variability in the Arctic clearly demonstrates that the the modern rapid ice loss over the past century does not fit with historical patterns over the past 10,000 years. Now that temperatures are rising and Arctic sea ice coverage is decreasing, animals in the Pacific and Atlantic will once again be able to move northwards and intermingle. Increasing temperatures will largely affect shallow water fauna and those that live where deep water masses are exchanged with warmer surface water. The ability of animals to migrate, invade new ecosystems, and adapt to environmental change very over short timescales will depend very much on the changes of the physical environment in addition to the life history and temperature tolerances of each individual species. For example, animals that swim freely in the water column (as opposed to those that live on the sea floor) will have a greater ability to migrate north because surface waters are expected to warm more quickly than bottom waters. But what does this mean for incumbents of the Arctic? Not only will polar animals face potential challenges dealing with higher temperatures, they will also have to adjust to competition from invaders coming from warmer waters. In addition, the Arctic may experience changes in primary productivity as sea ice thins and light availability changes in this region. It is important to think about the changes occurring in the Arctic today in the context of those that have occurred in the past. From the past, we develop an understanding of how sea ice has changed previously and how ecosystems have responded, which enables a clearer picture of what our future Arctic may look like. |
ArchiveSea Levels: Past, Present and Future
How has El Niño changed in the past? Lessons from paleoclimate archives Paleoclimate into Policy: is there a bright future for learning from the past AuthorsWritten by the members of UC Davis GEL 232: K. Barclay, R. Banker, P. Edwards, C. Fish, K. Hewett, T. Hill, G. Hollyday, C. Livsey, H. Palmer, P. Shukla, D. Vasey. Categories
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