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Empirical-modelling perspectives on ice-retreat dynamics

Out today is a new publication in Earth Surface Dynamics written by myself and some colleagues that uses a fairly unique approach in the interpretation of palaeo ice-sheet dynamics. The setting for the research is Tremadog Bay in the Irish Sea Basin, a location close to the the confluence zone of the Irish Sea Ice Stream (a glacier that flowed southwards as far as the Scilly Isles) and the Welsh Ice Cap.

Tremadog Bay, Wales
Tremadog Bay, Wales

The study brought together empirical evidence from a variety of sources, including new mapping of glacial landforms found offshore, interpretations of glacial sediments from coastal exposures, and offshore borehole records from the wider bay area.

Landforms and sediments, however, usually only reflect glacial conditions during specific stages of advance or retreat, and can fail to fully represent how a glacier evolved and reacted through a whole glacial cycle. Numerical modelling data was therefore also used in combination to help interpret and tie together the various empirical datasets, and also help decipher a regional reconstruction of events during the last glaciation.

Readvance of the Welsh Ice Cap

Although the new geomorphology discovered on the floor of Tremadog Bay offered no real glaciological surprises, the major finding of the study was the inferred dynamics of the Welsh Ice Cap during deglaciation gained through insights from the numerical modelling.

Retreat of Welsh ice was episodic, reacting rapidly to minor fluctuations in the warming climate. Superimposed over these low-order oscillations of its margin though were asynchronous outlet readvances (above), driven by subtle time-transgressive variations in the mass balances of adjacent catchments. Numerical modelling experiments suggest the driver of this dynamic was internal, amplified via the migration of the ice cap’s main ice divide.

Ice-divide migration

The new geomorphological data also added further weight to the hypothesis that the large gravel sarns that extend from the Welsh coastline are indeed glacial, and Welsh in origin. Superimposed on their surface are elongated bedforms, associated with ice flow exiting from major valleys onshore.

In short, this study provides new insight into ice-sheet extent, dynamics and non-linear retreat across a major palaeo-ice stream confluence zone, offering useful perspectives on the interpretation of recent fluctuations observed by satellites over short timescales across analogous marine sectors of the Greenland and Antarctic ice sheets.


The paper is available by Open Access – meaning it is available to read by all. The abstract and PDF file is available from the journal Earth Surface Dynamics webpage.

 

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