CORRELATING WAVE POWER WITH GRAINSIZE OF ACCUMULATING SEDIMENT:DEVELOPMENT OF A PALEO PROXY FOR THE PACIFIC NORTHWEST CONTINENTAL SHELF

Mounting evidence indicates that climate change is impacting the heat budget of the oceans, which in turn has the potential to affect storm intensity and wave power. While observations of increasing storm intensity are now global, some of the earliest buoy evidence for changing wave climate comes from the Pacific Northwest margin, where buoy observations indicate annual average Significant Wave Height (SWH) is increasing at a rate of 1.5 ± 1 cm/yr with winter waves increasing at a faster rate over the past 40 years (Ruggiero et al. 2010). On the PNW margin these current systems are closely tied to the prevailing wave climate (Sternberg 1986). In theory, in the absence of changes in sediment supply, the size of transported grains will scale to the energy of bottom currents, thus offering a potential paleo proxy for prevailing wave climate. Preliminary observations of a late 20^th century increase in grain size of transported sediments have been made from the mid-shelf mud belt of the Columbia River (Robles-Rivera et al., 2017), although the sediment supply of this system is heavily modified via damming and thus the origin of these observations is ambiguous and must be corroborated. Here we analyze ~100 years of depositional history from three sediment cores from the mid-shelf mud belt of the undammed Umpqua River system using grain size of sortable silts and/or weight percentage of sand interpreted on an independent ²¹⁰Pb chronology. We will evaluate changes in sediment grain size in the Umpqua system against the observations from the Columbia mid-shelf mud belt as well as regional buoy data over the historic period. If this approach is successful and an apparent correlation of grain size with wave power is observed in two different regional sediment dispersal systems, we will be able to extend the independently dated reconstruction of PNW wave climate back ~100 years, improving our understanding of what may drive these changes.