Antarctic Peninsula - Climate Change

Climate Change

Because of issues concerning global climate change, the Antarctic Peninsula and adjacent parts of the Weddell Sea and its Pacific continental shelf has been the subject of intensive geologic, paleontologic, and paleoclimatic research by interdisciplinary and multinational groups over the last several decades. The combined study of the glaciology of its ice sheet and the paleontology, sedimentology, stratigraphy, structural geology, and volcanology of glacial and nonglacial deposits of the Antarctic Peninsula has allowed the reconstruction of the paleoclimatology and prehistoric ice sheet fluctuation of it for over the last 100 million years. This research shows the dramatic changes in climate, which have occurred within this region after it reached its approximate position within the Arctic Circle during the Cretaceous Period.

The Fossil Bluff Group, which outcrops within Alexander Island, Antarctic Peninsula, provides a detailed record, which includes paleosols and fossil plants, of middle Cretaceous (Albian) terrestrial climates. The sediments that form the Fossil Bluff Group accumulated within a volcanic island arc, which now forms the bedrock backbone of the Antarctic Peninsula, in prehistoric floodplains and deltas and offshore as submarine fans and other marine sediments. As reflected in the plant fossils, paleosols, and climate models, the climate was warm, humid, and seasonally dry. According to climate models, the summers were dry and winters were wet. The rivers were perennial and subject to intermittent flooding as the result of heavy rainfall.

Warm high-latitude climates reached a peak during the mid-Late Cretaceous Cretaceous thermal maximum. Plant fossils found within the Late Cretaceous (Coniacian and Santonian-early Campanian) strata of the Hidden Lake and Santa Maria formations, which outcrop within James Ross, Seymour, and adjacent islands, indicate that this emergent volcanic island arc enjoyed warm temperate or subtropical climates with adequate moisture for growth and without extended periods of below freezing winter temperatures.

After the peak warmth of Cretaceous thermal maximum, the climate, both regionally and globally, appears to have cooled as seen in the Antarctic fossil wood record. Later, warm high-latitude climates returned to the Antarctic Peninsula region during the Paleocene and early Eocene as reflected in fossil plants. Abundant plant and marine fossils from Paleogene marine sediments that outcrop on Seymour Island indicate the presence of cool and moist, high-latitudes environment during the early Eocene.

Detailed studies of the paleontology, sedimentology, and stratigraphy of glacial and nonglacial deposits within the Antarctic Peninsula and adjacent parts of the Weddell Sea and its Pacific continental shelf have found that it has become progressively glaciated as the climate of Antarctica dramatically and progressively cooled during the last 37 million years. This progressive cooling was contemporaneous with a reduction in atmospheric CO2 concentrations. During this climatic cooling, the Antarctic Peninsula was likely the last region of Antarctica to have been fully glaciated. Within the Antarctic Peninsula, mountain glaciation was initiated during the latest Eocene, about 37–34 Ma. The transition from temperate, alpine glaciation to a dynamic ice sheet occurred about 12.8 Ma. At this time, the Antarctic Peninsula formed as the bedrock islands underlying it were overridden and joined together by an ice sheet in the early Pliocene about 5.3–3.6 Ma. During the Quaternary Period, the size of the West Antarctic Ice Sheet has fluctuated in response to glacial - interglacial cycles. During glacial epochs, this ice sheet was significantly thicker than it is currently is and extended to the edge of the continental shelves. During interglacial epochs, the West Antarctica Ice Sheet was thinner than during glacial epochs and its margins lay significantly inland of the continental margins.

During the Last Glacial Maximum, about 20,000 to 18,000 years ago, the ice sheet covering the Antarctic Peninsula was significantly thicker than it is now. Except for a few isolated nunataks, the Antarctic Peninsula and its associated islands were completely buried by the ice sheet. In addition, the ice sheet extended past the present shoreline onto the Pacific outer continental shelf and completely filled the Weddell Sea up to the continental margin with grounded ice.

The deglaciation of the Antarctic Peninsula largely occurred between 18,000 to 6,000 years ago as an interglacial climate was established in the region. It initially started about 18,000 to 14,000 years ago with retreat of the ice sheet from the Pacific outer continental shelf and the continental margin within the Weddell Sea. Within the Weddell Sea, the transition from grounded ice to a floating ice shelf occurred about 10,000 years ago. The deglaciation of some locations within the Antarctic Peninsula continued until 4,000 to 3,000 years ago. Within the Antarctic Peninsula, an interglacial climatic optimum occurred about 3,000 to 5,000 years ago. After the climate optimum, a distinct climate cooling, which lasted until historic times, occurred.

The Antarctic Peninsula is a part of the world that is experiencing extraordinary warming. Each decade for the last five, average temperatures in the Antarctic Peninsula have risen by half a degree Celsius. Ice mass loss on the peninsula occurred at a rate of 60 billion tonnes in 2006, with the greatest change occurring in the northern tip of the peninsula. Seven ice shelves along the Antarctic Peninsula have retreated or disintegrated in the last two decades. Research by the United States Geological Survey has revealed that every ice front on the southern half of the peninsula experienced a retreat between 1947 and 2009. According to a study by the British Antarctic Survey, glaciers on the peninsula are not only retreating but also increasing their flow rate as a result of increased buoyancy in the lower parts of the glaciers. Professor David Vaughan has described the disintegration of the Wilkins Ice Shelf as the latest evidence of rapid warming in the area. The Intergovernmental Panel on Climate Change has been unable to determine the greatest potential effect on sea level rise that glaciers in the region may cause.

See also: Antarctica cooling controversy and Retreat of glaciers since 1850