Late Holocene seasonal temperature variability of the western Scottish shelf (St Kilda) recorded in fossil shells of the bivalve Glycymeris glycymeris
Graphical abstract
Introduction
The North Atlantic is a key region in the global climate system. The Atlantic Meridional Overturning Circulation (AMOC) plays a crucial role in the global redistribution of heat, carbon, and nutrients, and has been implicated in abrupt climatic shifts (Buckley and Marshall, 2015). In addition to the main North Atlantic basin, shelf seas are an integral part of the North Atlantic region. Shelf seas are in exchange with the open ocean, and disproportionately important for primary production and the sequestration of atmospheric carbon (Chen et al., 2013). Thus, understanding the dynamics and natural variability of the Atlantic circulation and adjacent shelf seas is crucial to understanding past and future climate changes.
North Atlantic sea surface temperatures (SST) have been decreasing since 5700 years before present (yr BP), which is generally linked to an orbitally forced decrease in solar irradiance (e.g. Marchal et al., 2002). However, SST trends and variability in the late Holocene are temporally and spatially heterogenous, due to processes in the different limbs of the AMOC and regional ocean-atmosphere feedbacks (e.g. Moffa-Sánchez et al., 2014; Solignac et al., 2008). In the fourth millennium BP, solar activity was relatively low, with a strong negative excursion noted at ca. 3.4 kyr BP (Steinhilber et al., 2012, 2009). The atmospheric conditions in the fourth millennium BP are thought to have been dominated by a weakly positive North Atlantic Oscillation (NAO) with several negative phases (Goslin et al., 2018; Olsen et al., 2012; Orme et al., 2017). A low-to-negative NAO is associated with a southward-shifted storm track and a southward-shifted and weaker North Atlantic Current (NAC; Curry and McCartney, 2001; Taylor and Stephens, 1998). However, reconstructed long-term trends of the NAO and storm track positions cannot provide a full picture of their high-frequency variability. For example, aeolian sediment reconstructions from the Outer Hebrides, Scotland, indicate strong westerly wind activity at ca. 3.3 cal kyr BP (Gilbertson et al., 1999; Orme et al., 2016), which could have caused increased Atlantic inflow on the Hebrides Shelf (Jones et al., 2020, 2018).
Traditional palaeoceanographic studies have mainly focussed on changes over millennia (Lynch-Stieglitz et al., 2007). However, instrumental observations of the AMOC show pronounced changes in the system on decadal scales (Robson et al., 2014). Thus, a dense network of proxies for past high-frequency variability of the AMOC is required to complement existing records of past climatic changes and to build a bridge to modern observations (Ninnemann and Thornalley, 2016). Moreover, hydroclimatic variability of the British Isles in the late Holocene has predominantly occurred on the decadal-to-centennial scale, with strong links to changes in North Atlantic ocean circulation (Charman, 2010; Swindles et al., 2013). While terrestrial records tend to be more highly resolved due to fast sedimentation rates, marine records of equivalent resolution are rather scarce (Charman and McCarroll, 2010). Hence, to investigate and constrain marine-terrestrial relationships further, highly resolved marine records are needed; records from shelf seas are of particular interest as they are more tightly coupled with the adjacent terrestrial environment.
In recent decades, bivalve sclerochronology has emerged as a new research field with important applications in the study of highly resolved past marine variability (e.g. Jones, 1983; Schöne et al., 2005). The annual growth increments in long-lived bivalves reflect the environment the animals live in and can be crossmatched between specimens to construct multi-centennial chronologies (e.g. Butler et al., 2013). When live-collected specimens are incorporated into a chronology, the absolute calendar year of each annual increment is known and, through accurate crossmatching, dating uncertainties within the record can be virtually eliminated (Black et al., 2019). However, when working with fossil shells, it is not always possible to incorporate live-collected specimens into the chronology. Instead, crossmatched fossil shells build a “floating chronology”, which is not anchored in time (Scourse et al., 2006). While this means that floating chronologies do not provide absolute calendar dates, the growth records are annually resolved and, most importantly, replicated. Thus, floating chronologies provide valuable and robust high-resolution records of past environmental variability.
Previous studies have demonstrated that the long-lived bivalve Glycymeris glycymeris is a potential target for reconstructing climate variability in the North Atlantic region (Brocas et al., 2013; Featherstone et al., 2020; Reynolds et al., 2013; Royer et al., 2013). G. glycymeris can live for almost 200 years (Reynolds et al., 2013) as a shallow burrower in preferably coarse sediment like gravel or gravelly sand at depths up to 100 m (Thomas, 1975, and references therein). Shell growth occurs synchronously among specimens and populations that are exposed to the same environmental factors, which renders sclerochronological studies possible (Brocas et al., 2013; Reynolds et al., 2013). The growth increments are delimited by organic-rich growth lines that are formed each year when shell growth slows down drastically shortly after the temperature peak (e.g. Reynolds et al., 2017). Whether shell growth continues at a very slow rate throughout this “off season” or ceases completely at one point is not known, but any information that might be stored in the annual growth lines is inaccessible to current sampling techniques. Consequently, “annual” G. glycymeris growth records do not represent the entire year, but are instead biased towards the warmer months of the year. This seasonal bias is a common characteristic of bivalve chronologies at mid- to high latitudes (Killam and Clapham, 2018), and is usually regarded as a limitation. However, many climatic patterns and shifts result from processes that are also seasonally biased (e.g seasonal flux of solar energy), and annual averages of past climatic and environmental conditions mask such seasonal-scale variability (Carré and Cheddadi, 2017). Thus, seasonal bias in the growth record can potentially be used as an asset when the exact timing of the growth season is known. The growth season can be determined through sub-annual oxygen isotope samples of the shell carbonate (δ18Oc), which are calibrated against instrumental temperature records (e.g. Weidman et al., 1994). Furthermore, the sub-annual δ18Oc series can provide insight into inter-annual variability of the respective growth season through time (Schöne and Fiebig, 2009; Wanamaker et al., 2011).
Here, we present a floating, crossmatched G. glycymeris chronology and associated sub-annual δ18Oc profiles from the Hebrides Shelf, NW Scotland, radiocarbon dated to the fourth millennium BP. The fossil δ18Oc series are compared to those of modern specimens from the same sample site. The aim of this study is to investigate seasonality and seawater temperatures on the Hebrides Shelf in the late Holocene and, in so doing, add to existing data on past marine variability in the Northeast Atlantic.
Section snippets
The Hebrides Shelf
The Hebrides Shelf is located to the west of Scotland; the shelf edge extends from ca. 56° N to 60° N. The shelf slopes gently to the west of the Outer Hebrides until a water depth of 120–140 m is reached in the vicinity of the archipelago of St Kilda (Sutherland et al., 1984). The shelf edge is steep; to the west of the edge lies the Rockall Trough, which reaches depths of 2000 m at this latitude (Holliday et al., 2000).
The shelf sea is influenced by Atlantic waters through shelf-ocean
Sample site and material
The material for this study was collected at Village Bay, St Kilda, during a research cruise aboard the RV Prince Madog in May 2014 (Fig. 1). Apart from seven young live G. glycymeris specimens, most of the material consisted of single G. glycymeris valves (n = 645). All samples were collected at 40–65 m depth in parallel tows using a customised dredge of 1 m width (for a description see Butler et al., 2009b). The dead-collected samples presented in this paper were collected in two neighbouring
Floating chronology
The floating chronology was constructed with seven dead-collected G. glycymeris from St Kilda. Because this chronology is not absolutely dated, the time axes are reported in relative chronology years (Fig. 3).
The increments of the hinge plate in the first 10–20 ontogenetic years were narrow and often contained the spurious lines sometimes known as “doublets” (Butler et al., 2009a), which complicated crossmatching. Thus, the first 20 years of each specimen were excluded from further analysis.
Chronology
Seven fossil G. glycymeris were crossmatched based on their annual growth patterns, building a floating chronology. Six of the crossmatched shells were later radiocarbon dated, consistently placing all specimens in the 4th millennium BP, thus confirming that they were approximately coeval.
A G. glycymeris chronology and annual δ18Oc series covering the last two centuries have previously been published for the Tiree Passage, Inner Hebrides (Reynolds et al., 2017, 2013). To our knowledge, ours is
Conclusions
We present here a 187-year growth chronology from the fourth millennium BP at St Kilda, western Scotland, based on fossil G. glycymeris shells. Sub-annual δ18Oc records from fossil specimens of the floating chronology and from modern specimens were used to compare growth season and seasonality between the two time periods. St Kilda is appropriately sited to study the variability of North Atlantic inflow as it is an offshore location close to the shelf margin, with negligible freshwater input.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
This work was funded by the EU within the framework of the Marie Curie Initial Training Network ARAMACC (project GA604802). Micro-Raman spectroscopy was undertaken as part of a rapid access request to the Diamond Light Source (SP13616-1). We thank the crew of the RV Prince Madog for the support during the research cruise, and our ARAMACC colleagues for the help with sample collection. Many thanks to Paula J. Reimer, Ron Reimer, and Julia Simpson for hosting SJA at the 14CHRONO Centre, and for
References (125)
Shell midden sclerochronology
Quat. Sci. Rev.
(2011)- et al.
Can earthworm secreted calcium carbonate immobilise Zn in contaminated soils?
Soil Biol. Biochem.
(2014) - et al.
The dog cockle, Glycymeris glycymeris (L.), a new annually-resolved sclerochronological archive for the Irish Sea
Palaeogeogr. Palaeoclimatol. Palaeoecol.
(2013) - et al.
Continuous marine radiocarbon reservoir calibration and the 13C Suess effect in the Irish Sea: results from the first multi-centennial shell-based marine master chronology
Earth Planet. Sci. Lett.
(2009) - et al.
Variability of marine climate on the North Icelandic Shelf in a 1357-year proxy archive based on growth increments in the bivalve Arctica islandica
Palaeogeogr. Palaeoclimatol. Palaeoecol.
(2013) - et al.
Is there a reliable taphonomic clock in the temperate North Atlantic? An example from a North Sea population of the mollusc Arctica islandica
Palaeogeogr. Palaeoclimatol. Palaeoecol.
(2020) Centennial climate variability in the British Isles during the mid-late Holocene
Quat. Sci. Rev.
(2010)- et al.
Climate variability of the British Isles and adjoining seas
Quat. Sci. Rev.
(2010) - et al.
Controls on the stable isotope composition of seasonal growth bands in aragonitic fresh-water bivalves (Unionidae)
Geochim. Cosmochim. Acta
(1999) - et al.
Monthly distributions of surface and bottom temperatures in the northwest European shelf seas
Cont. Shelf Res.
(1991)
The oxygen isotope composition of water masses in the northern North Atlantic
Deep Res. I
Strontium/lithium ratio in shells of Cerastoderma edule (Bivalvia) – a new potential temperature proxy for brackish environments
Chem. Geol.
Late Holocene land- and sea-level changes in the British Isles: Implications for future sea-level predictions
Quat. Sci. Rev.
Sand-drift and soil formation along an exposed North Atlantic Coastline: 14,000 years of diverse geomorphological, climatic and human impacts
J. Archaeol. Sci.
Oxygen and carbon isotope fractionation in biogenic aragonite: temperature effects
Chem. Geol. (Isotope Geosci. Sect.)
Stone Age midden deposition assessed by bivalve sclerochronology and radiocarbon wiggle-matching of Arctica islandica shell increments
J. Archaeol. Sci.
On the oceanographic variability of the North-West European Shelf to the West of Scotland
J. Mar. Syst.
Decadal variability on the Northwest European continental shelf
Prog. Oceanogr.
Apparent long-term cooling of the sea surface in the Northeast Atlantic and Mediterranean during the Holocene
Quat. Sci. Rev.
Aeolian sediment reconstructions from the Scottish Outer Hebrides: late Holocene storminess and the role of the North Atlantic Oscillation
Quat. Sci. Rev.
Subpolar North Atlantic Sea surface temperature since 6 ka BP: Indications of anomalous ocean-atmosphere interactions at 4–2 ka BP
Quat. Sci. Rev.
Diagenesis of mollusc aragonite and the role of fluid reservoirs
Earth Planet. Sci. Lett.
Seasonality of the European slope current (Goban Spur) and ocean margin exchange
Cont. Shelf Res.
Cross-slope flow in the Atlantic Inflow Current driven by the on-shelf deflection of a slope current
Deep Res. Part I Oceanogr. Res. Pap.
A multiproxy reconstruction of Hebridean (NW Scotland) spring sea surface temperatures between AD 1805 and 2010
Palaeogeogr. Palaeoclimatol. Palaeoecol.
Oxygen isotope composition of seawater
Structural analysis and paleoenvironmental potential of dog cockle shells (Glycymeris glycymeris) in Brittany, Northwest France
Palaeogeogr. Palaeoclimatol. Palaeoecol.
Arctica islandica (Bivalvia): a unique paleoenvironmental archive of the northern North Atlantic Ocean
Glob. Planet. Chang.
Climate records from a bivalved Methuselah (Arctica islandica, Mollusca; Iceland)
Palaeogeogr. Palaeoclimatol. Palaeoecol.
Holocene evolution of seasonal stratification in the Celtic Sea: refined age model, mixing depths and foraminiferal stratigraphy
Mar. Geol.
Ecological investigations with the Undulating Oceanographic Recorder: the hydrography and plankton of the waters adjacent to the Orkney and Shetland Islands
Mar. Biol.
Late glacial sedimentology, foraminifera and stable isotope stratigraphy of the Hebridean Continental Shelf, Northwest Scotland
Evolution of seasonal stratification in the Celtic Sea during the Holocene
J. Geol. Soc. Lond.
Mid-latitude shelf seas: a NW European perspective on the seasonal dynamics of temperature, salinity and oxygen isotopes
The Holocene
Holocene palaeoclimate records from peatlands
A decadal-scale Holocene Sea surface temperature record from the subpolar North Atlantic constructed using diatoms and statistics and its relation to other climate parameters
Paleobiol.
The revolution of crossdating in marine palaeoecology and palaeoclimatology
Biol. Lett.
Comparison of gridded sea surface temperature datasets for marine ecosystem studies
Mar. Ecol. Prog. Ser.
Bayesian analysis of radiocarbon dates
Radiocarbon
‘Wiggle matching’ radiocarbon dates
Radiocarbon
Observations, inferences, and mechanisms of the Atlantic Meridional Overturning Circulation: a review
Rev. Geophys.
Accurate increment identification and the spatial extent of the common signal in five Arctica islandica chronologies from the Fladen Ground, northern North Sea
Paleoceanography
Seasonality in long-term climate change
Quaternaire
Air–sea exchanges of CO2 in the world’s coastal seas
Biogeosciences
Effect of diagenesis on the Sr, O, and C isotope composition of late cretaceous mollusks from the western interior seaway of North America
Am. J. Sci.
A Time Series Analysis Approach to Tree Ring Standardization
Program ARSTAN: A Tree-Ring Standardization Program Based on Detrending and Autoregressive Time Series Modeling, with Interactive Graphics
Tree-ring standardization and growth-trend estimation
The shell ultrastructure of the genus Glycymeris Da Costa, 1778: a comparison between fossil and recent specimens
Riv. Ital. Paleontol. Stratigr.
Ocean gyre circulation changes associated with the North Atlantic Oscillation
J. Phys. Oceanogr.
Cited by (3)
Developing a sclerochronology network in the Adriatic Sea: Growth synchrony among populations of Callista chione
2023, Regional Studies in Marine ScienceReading the diaries of life – Current advances in sclerochronological research
2021, Palaeogeography, Palaeoclimatology, Palaeoecology