Alkenones, alkenoates, and organic matter in coastal environments of NW Scotland: Assessment of potential application for sea level reconstruction

Abstract

[1] Reconstruction of late Quaternary sea level history in areas of glacioisostatic uplift often relies on sediment archives from coastal isolation basins, natural coastal rock depressions previously isolated from or connected to the sea at different times. Proxy indicators for marine, brackish, or lacustrine conditions combined with precise dating can constrain the time when the sea crossed the sill threshold and isolated (or connected) the basin. The utility of isolation basins in investigations of sea level change is well known, but investigations have been mostly limited to microfossil proxies, the application of which can be limited by preservation and nonanalog problems. Here we investigate the potential of long-chain alkenones, alkenoates, and bulk organic parameters (TOC, C org /N) for reconstructing past sea level changes in isolation basins in NW Scotland. We analyze organic biomarkers and bulk parameters from both modern basins (at different stages of isolation from the sea) and fossil basins (with sea level histories reconstructed from established proxies). Logit regression analysis was employed to find which of the biomarker metrics or bulk organic measurements could reliably characterize the sediment samples in terms of a marine/ brackish or isolated/lacustrine origin. The results suggested a good efficiency for the alkenone index %C 37:4 at predicting the depositional origin of the sediments. This study suggests that alkenones could be used as a novel proxy for sea level change in fossil isolation basins especially when microfossil preservation is poor.

Alkenone Paleothermometry in Coastal Settings: Evaluating the Potential for Highly Resolved Time Series of Sea Surface Temperature

“…Normal March–April salinities in this part of the Bay are generally ≥24 psu. These results are consistent with those detecting high contributions of C 37:4 alkenones in other lower salinity ecosystems (Bendle et al, ; Blanz et al, ; Ficken & Farrimond, ; Mercer et al, ; Schulz et al, ; Schwab & Sachs, ; Warden et al, ) and suggest that a cutoff may exist near 25 psu, below which pelagic Group III haptophytes are outcompeted by other (Group I and/or II) alkenone producers, in Narragansett Bay.…”

“…Previous studies document the temperature dependence in the ratios of di‐unsaturated to tri‐unsaturated 37‐carbon alkenone biomarkers produced by coccolithophorids in pelagic, marginal, and coastal waters and sediments (Bendle et al, ; Blanz et al, ; Conte et al, ; Ficken & Farrimond, ; Marlowe et al, ; Mercer et al, ; Müller et al, ; Warden et al, ). Pelagic alkenones are produced by Group III (following the phylogenetic naming convention of Theroux et al, ) haptophyte algae, primarily Emiliania huxleyi and Gephyrocapsa oceanica (Conte et al, ; De Leeuw et al, ; Volkman et al, ).…”

“…While alkenone ratios appear to be sensitive to modern and historical SST change in high salinity (≥30 psu) marginal and coastal systems (Framvaren Fjord, Norway (Ficken & Farrimond, ) and the Skagerrak, North Sea (Blanz et al, )), their relationship to SST breaks down in brackish (0.5–30 psu) systems (Bendle et al, ; Blanz et al, ; Ficken & Farrimond, ; Mercer et al, ; Warden et al, ). This is likely caused by salinity‐driven shifts in the alkenone producing population.…”

A multi-proxy approach to assessing isolation basin stratigraphy from the Lofoten Islands, Norway

“…This method is more rapid, but also has limitations such as selective degradation of organic matter and can be affected by large external environmental changes including atmospheric pCO 2 , vegetation development, and temperature (Lamb et al, 2006;Mackie et al, 2007). Others have also explored the use of molecular biomarkers (Bendle et al, 2009) as indicators of surface water salinity and scanning X-ray fluorescence (XRF) (Sparrenbom et al, 2006) to identity physical sedimentary changes.…”

Fjord systems and archives: a review

“…In polar fjords this technique is also being used. The lipid present in the algae in sea ice has the potential to provide estimates of polar ice and temperature throughout the Holocene (Bendle et al 2009). Given the uncertainty in estimating the rate and impact of present global warming, Holocene fjord records can be a valuable predictive tool through the high-resolution insights they can provide on previous rapid climatic change.…”