System responses to Holocene relative sea-level rise and sediment supply in a macrotidal estuary

Abstract

Estuaries are at the interface of marine and terrestrial systems and as such, are subject to environmental change arising from multiple driving mechanisms, with the interplay between the dominant controls varying spatially and temporally. Relative sea-level (RSL) change and sediment supply can play a significant role in driving environmental change. This study examines the relative influence of these drivers during the Holocene. Biostratigraphic records and RSL data are presented from two locations in the inner portion and upper reaches of the macrotidal Humber Estuary, eastern England. The results provide a new terrestrial limiting point and six sea-level index points, two of which at c. 1500 cal years BP provide the youngest sea-level index points for the inner estuary. An early-mid Holocene tidal lagoon system, that lacks modern equivalent, is recorded at one site. The results indicate a shift in the dominance of RSL rise driving the early Holocene creation of wetlands, to sediment supply dominating changes in the mid-late Holocene against the backdrop of a reduced rate of RSL rise, with a submergence of wetlands evident after c. 4000 cal years BP. The persistence of fen carr evident between c. 6800 and 5500 cal years BP suggests stability and resilience of the peatland system to continuing RSL rise. As rates of contemporary RSL rise increase, combined with climate and human impacts on the landscape, the drivers of change in these type of estuary systems will shift, with the records providing analogues of potential system responses that can help inform coastal management strategies.

Coastal Lagoonal Evolution within the Early Holocene Humber Estuary, eastern England

“…The classification scheme of Vos and de Wolf (1993) suggests that, for the duration of sedimentation taking place in the locale surrounding these three vibrocores, between c. 9100 and 8100 cal a bp , deposition took place in a tidal lagoon. The presence of laminated deposits supports the interpretation of a lagoonal deposit, similar to that observed by Best et al (2022) within the Inner Estuary. Taking into account the location of the offshore vibrocores, there is an apparent fall in taxa associated with freshwater conditions further landward, from GT2‐08‐VC through to GT2‐06‐VC.…”

“…The sedimentary sequences from the nearshore zone at Horseshoe Point provide a unique glimpse into the Early Holocene dynamics of the Outer Humber Estuary during a period of rapid RSL rise. Like the record from Hook Lane (Best et al, 2022), the environmental transition that occurred was in response to the Early Holocene rapid RSL rise, with a significant increase in accommodation space, that inundated the existing wetland surface, leading to the formation of a tidal lagoonal system. Shifts in saline influence between and within cores infer that, although discrete and short timeframes are being analysed in each stratigraphic sequence, evidence of increasing saline influence over time is apparent, being driven by the rapid rate of Early Holocene RSL.…”

“…The Horseshoe Point deposits can be compared with the recently discovered Early Holocene site at Hook Lane, within the Inner Humber Estuary, where Best et al (2022) identified the development of perimarine tidal lagoonal deposits. Like the record from Horseshoe Point, an initial short‐lived fen carr environment is replaced by an influx of inorganic sediment corresponding with a reduction in Alnus pollen.…”

“…Like the record from Horseshoe Point, an initial short‐lived fen carr environment is replaced by an influx of inorganic sediment corresponding with a reduction in Alnus pollen. Best et al (2022) attributed this to the rapid rise in RSL, creating increased accommodation space, leading to flooding, submergence and eventually the creation of an expansive tidal lagoonal system, dated c. 7800 cal a bp at Hook Lane. The discovery of perimarine tidal lagoonal sites is uncommon, lacking any modern equivalent in NW Europe today, so evidence for two locations within the Humber Estuary, close in age, may be significant, suggesting that different coastal lowland conditions prevailed within this area during the Early Holocene.…”

“…They also propose that the Lincolnshire coast contained several till headlands, now eroded, which extended north from the modern coastline; such landforms might have also facilitated barrier formation and lagoonal development. At Hook Lane, Best et al (2022) proposed that the initial flooding of the fen carr environment, in response to RSL rise, was coupled with an expansion of accommodation space as water levels rose but sedimentation rates were unable to keep pace with this rise, leading to flooding, submergence and eventually the creation of expansive tidal lagoonal conditions. At both Hook Lane and Horseshoe Point, Alnus pollen declines across the transition from organic to inorganic deposition and lagoonal initiation, along with a change in the diatom biostratigraphy from initially freshwater and perimarine in nature, reflecting the role of rising water tables and impeded fluvial drainage in the creation of these features.…”