Thermal history of the Arctic Ocean environs adjacent to North America during the last 3.5 Ma and a possible mechanism for the cause of the cold events (major glaciations and permafrost events)

Abstract

At 3.5 Ma, the Arctic Ocean was unfrozen, and only during the second Pliocene cold event (Californian - 3.0 Ma) did an extensive glaciation occur in Alaska-Yukon and Iceland. The sea froze during the third (Alaskan - 2.58 Ma) event as the western Arctic cooled rapidly. Baffin Island and Labrador were the centres of ice sheets, and ice-rafted debris appeared in the North Atlantic. Shrub-tundra replaced boreal forest in the west during the next warm episode but forested-shrubtundra persisted in north Greenland during the next (Wyoming - 2.2 Ma) cold event. During the last Pliocene (Montanan - 1.9 Ma) cold event, tundra surrounded the Arctic basin with widespread permafrost in unglaciated areas. Quaternary cold events were more frequent, with tundra persisting on land during warm episodes, although coastal seas usually thawed seasonally. There was a continuous cooling trend due to the demise of the Tethyan sea, but the ¹⁸O marine curve shows about 130 fluctuations compared with 14 major cold events on land. The cause of the terrestrial changes seems to be the interaction of many cyclical controls with different periodicities. When enough cycles are synchronized for air temperature to cross a critical threshold, a climatic change occurs. The critical thresholds are dependent on local environments and latitude.