Observations and modeling of fjord sedimentation during the 30 year retreat of Columbia Glacier, AK

KATHERINE BOLDT LOVE,BERNARD HALLET,SHAD O'NEEL,THOMAS L. PRATT

doi:10.1017/jog.2016.67

KATHERINE BOLDT LOVE, BERNARD HALLET + Show 2 more

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https://doi.org/10.1017/jog.2016.67

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Abstract

ABSTRACTTo explore links between glacier dynamics, sediment yields and the accumulation of glacial sediments in a temperate setting, we use extensive glaciological observations for Columbia Glacier, Alaska, and new oceanographic data from the fjord exposed during its retreat. High-resolution seismic data indicate that 3.2 × 108m3of sediment has accumulated in Columbia Fjord over the past three decades, which corresponds to ~5 mm a−1of erosion averaged over the glaciated area. We develop a general model to infer the sediment-flux history from the glacier that is compatible with the observed retreat history, and the thickness and architecture of the fjord sediment deposits. Results reveal a fivefold increase in sediment flux from 1997 to 2000, which is not correlated with concurrent changes in ice flux or retreat rate. We suggest the flux increase resulted from an increase in the sediment transport capacity of the subglacial hydraulic system due to the retreat-related steepening of the glacier surface over a known subglacial deep basin. Because variations in subglacial sediment storage can impact glacial sediment flux, in addition to changes in climate, erosion rate and glacier dynamics, the interpretation of climatic changes based on the sediment record is more complex than generally assumed.

Highlights

Over the past few decades, marine-ending glaciers around the world have lost mass at dramatic rates (e.g. Meier and Post, 1987; Rignot and Kanagaratnam, 2006; Pritchard and others, 2009; Shepherd and others, 2012)
Because mass loss from all Alaskan glaciers accounts for 20% of global ice loss (Gardner and others, 2013), Columbia alone accounts for ∼1% of global ice mass loss since the 1960s
To further explore the evolution of the sediment deposits in the fjord and the relationships between sediment delivery, sediment accumulation and redistribution, and glacier retreat, we developed a numerical model of fjord sedimentation over the 30 a retreat

Summary

Introduction

Over the past few decades, marine-ending (or tidewater) glaciers around the world have lost mass at dramatic rates (e.g. Meier and Post, 1987; Rignot and Kanagaratnam, 2006; Pritchard and others, 2009; Shepherd and others, 2012). Meier and Post, 1987; Rignot and Kanagaratnam, 2006; Pritchard and others, 2009; Shepherd and others, 2012) This widespread accelerated loss of ice into the ocean is attributed to an increase in rate of the interrelated processes of surface melting, iceberg calving and submarine melting at the glacier terminus. Together these processes cause glaciers to thin, accelerate and retreat (Meier and Post, 1987; Luckman and others, 2006; Howat and others, 2007; van den Broeke and others, 2009). The study of processes occurring along the critical ice/ocean boundary of tidewater glaciers, which can lose ice at an exceptional rate (e.g. Cogley, 2009) has broad scientific and societal relevance (e.g. Joughin and others, 2014; Rignot and others, 2014)

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