Transient, longitudinal, sedimentary furrows in the York River subestuary, Chesapeake Bay: Furrow evolution and effects on seabed mixing and sediment transport |
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| Authors: | Timothy M Dellapenna Steven A Kuehl Lillian Pitts |
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| Institution: | (1) Geology Department, Middlebury College, Middlebury, VT 05753, USA;(2) Earth Sciences, SUNY-Buffalo State College, Buffalo, NY 14222, USA |
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| Abstract: | Sedimentary furrows in fine-grained sediments have been observed in a variety of settings ranging from the deep ocean and
deep lake bottoms to shallow estuaries and are commonly described as persistent, long-term features of the seabed. A series
of 12 sidescan sonar surveys over the course of three years reveal that transient, longitudinal sedimentary furrows regularly
form and then occasionally dissipate within the middle portion of the York River. Varying furrow morphologies were observed
depending on current conditions, ranging from large regularly space (0.7–7 m) linear furrows during low current conditions
to large patches of meandering furrows as the mean current increases or no bed forms during the higher current conditions.
Based on210Pb and137Cs profiles of kasten cores, differences in physical mixing depths of ∼25 cm between cores collected <2 m apart indicate a
high degree of small-scale spatial heterogeneity within the seabed. By documenting the position of kasten cores using a digital
sidescan sonar system, we showed that a core taken within a furrow had a mixing depth 15 cm shallower than an adjacent core
taken between furrows. A time-series of mixing depths over the 35 mo of the study reveals that, along with the ∼25 cm scale
differences in mixing depths due to the formation and destruction of furrows, there is a longer temporal signal of mixing
producing 100-cm-scale changes in mixing depths on the annual to interannual time frame. Although the formation and destruction
of the furrows appear to be a significant process contributing to decimeter-scale seabed mixing, there is a longer-term unknown
process which is controlling the meter-scale seabed mixing. |
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