Abstract:
Variability in the terrigenous (land-derived) fraction of marine sediments,
including pollen and rock fragments, reflects the effects of regional climate change on
continentally derived runoff, ice extent, vegetation and ocean circulation. The transport of
this continental material to the seafloor must be understood in order to interpret the
terrigenous sediment record. This is investigated using several geochemical tracers to
identify transport pathways of material from Pacific Northwest rivers to continental
margin depositional sites.
We report the results of 40Ar/39Ar incremental heating and !Nd of bulk detrital
sediments (20-63" fraction) from core tops in an array of thirteen sites along the
continental margin of the Pacific Northwest. Geochemical signatures of sediment
transport along the continental margin are found to reflect proximal river sources reported
by VanLaningham et al. (2006), and the seasonal effect of northward flow in the
Davidson Current. This study provides the ‘proof of concept’ needed to describe downcore
changes in detrital sediment source and accumulation rate over the last 30ka at 3
sites within this array. Comparison of such changes to highly correlated variability in
pollen and plankton assemblages will distinguish terrestrial landscape changes from
changes in ocean circulation, as Pacific NW climate changed from glacial to present
conditions.
