Sudden Increase in Tidal Response Linked to Calving and Acceleration at a Large Greenland Outlet Glacier

Large calving events at Greenland's largest outlet glaciers are associated with glacial earthquakes and near instantaneous increases in glacier flow speed. At some glaciers and ice streams, flow is also modulated in a regular way by ocean tidal forcing at the terminus. At Helheim Glacier, analysis of geodetic data shows decimeter-level periodic position variations in response to tidal forcing. However, we also observe transient increases of more than 100% in the glacier's responsiveness to such tidal forcing following glacial-earthquake calving events. The timing and amplitude of the changes correlate strongly with the step-like increases in glacier speed and longitudinal strain rate associated with glacial earthquakes. The enhanced response to the ocean tides may be explained by a temporary disruption of the subglacial drainage system and a concomitant reduction of the friction at the ice-bedrock interface, and suggests a new means by which geodetic data may be used to infer glacier properties. Citation: de Juan, J., et al. (2010), Sudden increase in tidal response linked to calving and acceleration at a large Greenland outlet glacier, Geophys. Res. Lett., 37, L12501, doi: 10.1029/2010GL043289.

The Effects of Flowline Length Evolution on Chemistry-Delta O-18 Profiles from Penny Ice Cap, Baffin Island, Canada

The isotopic and chemical signatures for ice-age and Holocene ice from Summit, Greenland and Penny Ice Cap, Baffin Island, Canada, arc compared. The usual pattern of low delta(18)O, high Ca2+ and high Cl- is presented in the Summit records, but Penny Ice Cap has lower than present Cl- in its ice-age ice. A simple extension of the Hansson model (Hansson, 1994) is developed and used to simulate these signatures. The low ice-age Cl- from Penny Ice Cap is explained by having the ice-age ice originating many thousands of km inland near the centre of the Laurentide ice sheet and much further from the marine sources. Summit's flowlines all start close to the present site. The Penny Ice Cap early-Holocene delta(18)O's had to be corrected to offset the Laurentide meltwater distortion. The analysis suggests that presently the Summit and Penny Ice Cap marine impurity originates about,500 km away, and that presently Penny Ice Cap receives a significant amount of local continental impurity.

Tidal Flexure of Jakobshavns Glacier, West Greenland

Jakobshavns Glacier, a floating outlet glacier on the West Greenland coast, was surveyed during July 1976. The vertical displacements of targets along two profiles perpendicular to the fjord wall bounding the north margin of the glacier were analyzed to determine the effect of flexure caused by tidal oscillations within the fjord. An analysis based on the assumption that vertical displacements of the glacier reflected pure elastic bending yielded the conclusion that the effective thickness of the ice (i.e., the thickness which remained unaffected by surface and basal cracking and which behaved as a continuum) was ∼160 m 2.6 km upglacier from the calving front and ∼110 m 0.6 km from the calving front. An analysis based on the more realistic assumption that observed bending reflected elastic and viscoplastic deformation yielded the conclusion that the average effective thickness of the ice was 316 ± 74 m (∼40% of the estimated 800-m total thickness) 2.6 km from the calving front and 160 ± 48 m (∼21% of the estimated 750-m total) 0.6 km from the calving front. A constitutive relationship appropriate for hard glide during flexure was used.

A Modification of the Response Method of Tidal Analysis

An easily implemented extension of the standard response method of tidal analysis is outlined. The modification improves the extraction of both the steady and the tidal components from problematic time series by calculating tidal response weights uncontaminated by missing or anomalous data. Examples of time series containing data gaps and anomalous events are analyzed to demonstrate the applicability and advantage of the proposed method.

Nighttime Catches of Fishes in a Tidal Cove in Montsweag Bay Near Wiscasset Maine

Summer nighttime abundance and localized distribution of fishes in a tidal cove were studied by beach seining for comparison with a previous daytime study. American eels were relatively abundant at night and absent during the day. Alewife, blueback herring, and Atlantic silver-side were more abundant in the cove at night. Although mummichog numbers were greatly reduced at night, they remained an important constituent of the night fauna. Lesser components of the night fauna included Atlantic herring, Atlantic tomcod, smooth flounder, winter flounder, and rainbow smelt.

Twentieth Century Delta δC Variability in Surface Water Dissolved Inorganic Carbon Recorded by Coralline Algae in the Northern North Pacific Ocean and the Bering Sea

The oxygen isotopic composition and Mg/Ca ratios in the skeletons of long-lived coralline algae record ambient seawater temperature over time. Similarly, the carbon isotopic composition in the skeletons record delta(13)C values of ambient seawater dissolved inorganic carbon. Here, we measured delta(13)C in the coralline alga Clathromorphum nereostratum to test the feasibility of reconstructing the intrusion of anthropogenic CO(2) into the northern North Pacific Ocean and Bering Sea. The delta(13)C was measured in the high Mgcalcite skeleton of three C. nereostratum specimens from two islands 500 km apart in the Aleutian archipelago. In the records spanning 1887 to 2003, the average decadal rate of decline in delta(13)C values increased from 0.03% yr(-1) in the 1960s to 0.095% yr(-1) in the 1990s, which was higher than expected due to solely the delta(13)C-Suess effect. Deeper water in this region exhibits higher concentrations of CO(2) and low delta(13)C values. Transport of deeper water into surface water (i.e., upwelling) increases when the Aleutian Low is intensified. We hypothesized that the acceleration of the delta(13)C decline may result from increased upwelling from the 1960s to 1990s, which in turn was driven by increased intensity of the Aleutian Low. Detrended delta(13)C records also varied on 4-7 year and bidecadal timescales supporting an atmospheric teleconnection of tropical climate patterns to the northern North Pacific Ocean and Bering Sea manifested as changes in upwelling.

Summer Abundance of Fishes in a Maine Tidal Cove with Special Reference to Temperature

The daytime abundance and localized distribution of fishes in relation to temperature were studied in a small tidal cove by beach seining on seven dates in the Back River estuary, Maine, during the summers of 1971 and 1972. Temperatures on the seven dates ranged from 15.1–26.2 C, and salinities ranged from 17.3–24.7‰. Eighteen species of fishes were captured, with mummichogs, smooth flounders, Atlantic silversides and Atlantic herring together comprising over 98% of the catch. Mummichogs and Atlantic silversides were captured primarily near the inner end of the cove, while other abundant species were caught mainly at the outer end of the cove. Several species seem well adapted to naturally warm cove temperatures. Others seem now virtually excluded because of warm temperatures. Winter flounder, Atlantic herring, and Atlantic tomcod might be excluded from the cove during daytime in summer if artificial warming of the cove were permitted.