Alix G. Cage

Reconstructions of surface ocean conditions from the northeast Atlantic and Nordic seas during the last millennium

We undertake the first comprehensive effort to integrate North Atlantic marine climate records for the last millennium, highlighting some key components common within this system at a range of temporal and spatial scales. In such an approach, careful consideration needs to be given to the complexities inherent to the marine system. Composites therefore need to be hydrographically constrained and sensitive to both surface water mass variability and three-dimensional ocean dynamics. This study focuses on the northeast (NE) North Atlantic Ocean, particularly sites influenced by the North Atlantic Current. A composite plus regression approach is used to create an inter-regional NE North Atlantic reconstruction of sea surface temperature (SST) for the last 1000 years. We highlight the loss of spatial information associated with large-scale composite reconstructions of the marine environment. Regional reconstructions of SSTs off the Norwegian and Icelandic margins are presented, along with a larger-scale reconstruction spanning the NE North Atlantic. The latter indicates that the ‘Medieval Climate Anomaly’ warming was most pronounced before ad 1200, with a long-term cooling trend apparent after ad 1250. This trend persisted until the early 20th century, while in recent decades temperatures have been similar to those inferred for the ‘Medieval Climate Anomaly’. The reconstructions are consistent with other independent records of sea-surface and surface air temperatures from the region, indicating that they are adequately capturing the climate dynamics of the last millennium. Consequently, this method could potentially be used to develop large-scale reconstructions of SSTs for other hydrographically constrained regions.

Fjord systems and archives: a review

Abstract Fjords are glacially over-deepened semi-enclosed marine basins, typically with entrance sills separating their deep waters from the adjacent coastal waters which restrict water circulation and thus oxygen renewal. The location of fjords is principally controlled by the occurrence of ice sheets, either modern or ancestral. Fjords are therefore geomorphological features that represent the transition from the terrestrial to the marine environment and, as such, have the potential to preserve evidence of environmental change. Typically, most fjords have been glaciated a number of times and some high-latitude fjords still possess a resident glacier. In most cases, glacial erosion through successive glacial/interglacial cycles has ensured the removal of sediment sequences within the fjord. Hence the stratigraphic record in fjords largely preserves a glacial-deglacial cycle of deposition over the last 18 ka or so. Sheltered water and high sedimentation rates have the potential to make fjords ideal depositional environments for preserving continuous records of climate and environmental change with high temporal resolution. In addition to acting as high-resolution environmental archives, fjords can also be thought of as mini-ocean sedimentary basin laboratories. Fjords remain an understudied and often neglected sedimentary realm. With predictions of warming climates, changing ocean circulation and rising sea levels, this volume is a timely look at these environmentally sensitive coastlines. Supplementary material: The Glossary is available at: http://www.geolsoc.org.uk/SUP18440.

Marine radiocarbon reservoir ages in scottish coastal and fjordic waters

High freshwater inputs into Scottish sea lochs (fjords) combined with the restricted exchange between sea loch basin water and coastal Atlantic water masses are likely to result in reduced regional marine radiocarbon reservoir ages (R(t)) in these environments. To test this hypothesis, historical, museum-archived shells, collected live on known dates prior to AD 1950 from coastal locations in NW Scotland, were 14C dated to provide a means of determining R(t) and hence the regional deviation (∆R) from the modeled global surface ocean reservoir age (R). The sea loch data, when combined with 14C dates from the Scottish west coast (Harkness 1983), yield a regional ∆R value of -26 ± 14 yr. The ∆R of sea loch (fjordic) and coastal waters of NW Scotland are statistically different (at a confidence level >95%) from the ∆R value of 17 ± 14 yr reported for UK coastal waters (Reimer 2005; data after Harkness 1983) and are in good agreement with the coastal ∆R value of -33 ± 93 yr reported by Reimer et al. (2002). Therefore, it is recommended that a regional ∆R correction of -26 ± 14 yr should be applied to modern (i.e. pre-bomb but not prehistoric) marine 14C dates from the NW coast of Scotland.

Seasonal dynamics of coastal water masses in a Scottish fjord and their potential influence on benthic foraminiferal shell geochemistry

Abstract Pronounced seasonal heating of middle and high latitude shelf seas results in large temporal changes in seawater temperature that have the potential to be recorded by benthic foraminifera. Predicted oxygen isotope composition for calcite precipitating in equilibrium conditions with seawater suggest that pronounced ‘seasonal isotope effects’ may be encountered in the growth history of benthic foraminifera. Such ‘seasonal’ effects can be difficult to distinguish from so-called ‘vital effects’, where shell and equilibrium calcite values are offset by a constant difference in oxygen isotope values. Preliminary findings suggest that benthic foraminifera may have more than one phase of growth, for example Ammonia becarii calcifies in spring and late summer, potentially introducing apparent intra-annual and inter-annual temperature variations of >1°C into palaeoclimatic reconstructions when mixed-season populations are sampled. We highlight the need to select species-specific palaeotemperature equations to establish reliable isotopic disequilibria and illustrate the importance of understanding the ‘seasonal isotope effect’ when considering disequilibrium effects in foraminifera which have grown in seasonally-changing environments.

High benthic foraminiferal species counts in a Clyde Sea maerl bed, western Scotland

Abstract A preliminary investigation of the occurrence of hard-shelled benthic foraminifera in a sample of maerl (gravels derived from calcareous red seaweed) collected from a water depth of 10 m by SCUBA diving in the Clyde Sea, Scotland reveals an exceptionally well-preserved and diverse assemblage. A total of 90 different species were identified, comprising 12 agglutinated, 15 porcelaneous and 63 hyaline types; this represents the highest recorded species count described from the west of Scotland. The assemblage probably represents an integrated record of material derived directly from the maerl (mostly epifaunal types) and material derived from the reworking of adjacent sediments (mostly infaunal types). Maerl deposits represent an important near-shore habitat which appear to have been largely overlooked in regional studies of benthic foraminiferal distribution/ecology.