Late Holocene (ca. 4 ka) marine and terrestrial environmental change in Reykjarfjordur, north Iceland: climate and/or settlement?

Core B997-328PC is from the landward side of a 100-m-deep basin in Reykjarf jordur, a small fjord on the north coast of the northwest peninsula of Icel and. This is an area that can be severely affected by incursions of polar s ea-ice but has not suffered marked land erosion during the Settlement perio d. The core is 422 cm in length and consists principally of fine-grained mu ds with in situ molluscs. Eleven AMS C-14 dates on molluscs indicate a cons tant sediment accumulation rate of ca. 1 cm 10 yr(-1) for the last 4280 +/- 50 yr BP. We measured and derived a variety of proxies for indications of changes in the nearshore environment. These included physical properties an d grain size, mass accumulation rates, micropalaeontology (pollen and Foram inifera). Multivariate analysis and constrained clustering were used to def ine major changes in the proxies. In several parameters the major change in the fjord environment occurred close to 1000 C-14 yr ago, thus approximate ly coincident with the onset of the Settlement of Iceland. Other changes ar e noted at around 1600 and 3400 C-14 yr ago; Betula pollen disappears from the record ca. 1500 yr BP and there are peaks in marine productivity occurr ing ca. 2 and 3.4 ka. A major decline in carbonate accumulation and a sharp increase in the cold water benthic foraminifer Elphidium excavatum forma c lavata 400 yr ago represents the local marine signature of the Little Ice A ge. None of the changes in our data can be explained adequately by a simple call to land-use practices and an increase in land to sea transport, but b oth the pollen and foraminiferal records indicate a decrease and even loss of 'warm' elements in both flora and fauna over the past 4 kyr. Copyright ( C) 2001 John Wiley & Sons, Ltd.