Holocene paleoenvironmental reconstruction in Galway Bay, a shallow coastal embayment along Ireland’s North-East Atlantic margin

Abstract

Coastal environments are highly dynamic and complicated systems that vary spatially and temporally over a range of timescales. This study explores the paleoenvironmental changes recorded in sediment cores taken from Galway Bay, located on the coast of western Ireland. Galway Bay is a large shallow bay, which is protected from ocean swells of the North Atlantic by the Aran Islands. The inner bay receives freshwater mainly from the Corrib River Catchment. Four c. 6 m sediment cores were extracted along an inner bay transect and are explored here in a multi proxy paleoecological study to track environmental change during the Holocene period. Physical proxies obtained using a Multi Sensor Core Logger (MSCL), geochemical signatures acquired with X-ray fluorescence (XRF) scanning and microfossils (diatom and foraminifera) were examined. A Holocene timeframe was established with 23 AMS 14C dates across the four cores spanning c. 10000 cal years BP. A west-east progression is noted in the sediment stratigraphy. The western most sediment core contained no sediment post c. 8500 cal years BP while the eastern most sediment core, closest to the Corrib River outflow, contained the most complete sediment profile with sediments from the early, mid and late Holocene. A sedimentary hiatus spanning 5-7 ka is confirmed in two sediment cores. Change points in the sediment profiles are identified, reflecting known climatic events, including marine transgression, a possible 8.2 ka cooling event, freshwater phases and rising sea levels. The early Holocene encompassed the highest rate of sediment accumulation and marine transgression is captured in the proxy evidence. Coastal environmental change is postulated with water level rise and paleo tidal ranges varying from Highest Astronomical Tide to Mean High Water with high to middle marsh and mudflat development. The mid Holocene has a major break in sediment continuity with no complete mid Holocene sediment profile preserved. The innermost bay core retained sediment until c. 6000 cal years BP. The major hiatus is associated with a visible shell layer possibly reflecting a possible storm event and a sediment washout. The shell layer is overlain with late Holocene sediments (c. 500 years) in both inner bay cores reflecting either a return of conditions facilitating sediment deposition, or sediments that have not yet been washed out. The complex chronology and sedimentary profiles display a west to east progression along the inner Galway Bay transect reflecting a spatial trajectory of chronological, physical, chemical and biological change and thus environmental change as the rising sea made its way east into the Galway Bay.