The Holocene thermal maximum in the North American Arctic

Global databases of Holocene paleoclimates have been assembled, but these contain few data from the north American Arctic, especially from the High- and Mid-Arctic zones. A series of lake sediment cores from across the North American Arctic as well as data on treeline variations have been analyzed for several different proxy-climate data. The results show longitudinal differences in the timing of the maximum temperatures, with transitions synchronous across the North American Arctic, although not necessarily in the same direction. For example, at 8.2ka, the western and central Arctic cooled, but eastern Arctic and northern Greenland warmed. This space-time pattern of the Holocene Thermal Maximum (HTM) can be attributed to changes in the atmospheric circulation in response to the melting ice sheet, changes in the local energy balance in response to orbital insolation changes and other forcing.

The impacts of these changes on Arctic ecosystems are subtle but noticeable. Multiple proxies from the same core or from nearby lakes sometimes show coherent changes but at other times differences. For terrestrial ecosystems, biodiversity seems less affected by warmer conditions than biological production, which increased during local HTM. Periods of warm conditions and high terrestrial plant production were associated with a decrease in diatom production (as measured by accumulation rates) in some sites, and in some cases, with an absence of diatoms in the sediments (diatom-free zones), for reasons not yet clear. Secondary production of chironomid communities living in the lake sediments was sometimes coherent with diatom production, but not at other times.