The effects of beach energy on sediment entrainment within the nearshore ice complexLake core data

Abstract

Shore ice forms along beaches in cold climates and during its formation is capable of entraining sediment from the nearshore. Upon breakup, entrained sediment within the ice can be rafted to deeper waters, melt out and lost to the nearshore sediment budget. Previous studies have hypothesized that this sediment rafting could be a principal source of sediment loss from the nearshore sediment budget. However, fundamental questions remain about the primary mechanisms for entraining sediment within the ice, particularly differences between high and low energy beaches. In this study we collected a series of sixty-four ice cores from five different beaches along the Laurentian Great Lakes that spanned low to high energy regimes. These ice cores were analyzed for ice structure, sediment structure and entrained sediment mass. We found that low energy beaches primarily entrained sediment within the icefoot as the ice directly adhered sediments to its base. Conversely high energy beaches primarily entrained sediment when sediment laden water was washed atop the ice through wave action and subsequently incorporated into the ice structure. Overall, for a range of high energy beaches we find that in floating ice, sediment makes up approximately 1% of the total weight, which is nearly an order of magnitude greater than in low energy beaches (e.g., 0.1%). These findings provide a general description of the most important processes for sediment entrainment within nearshore ice for both high and low energy beaches, motivating a 1% approximation for estimating sediment budgets associated with shore ice.