The modern and late Holocene marine environments of Loch Sunart, N.W. Scotland

The first study to exploit the sedimentary archives of Loch Sunart, a relatively well-flushed fjord on the NW coast of Scotland, for palaeoenvironmental reconstruction is presented. In order to understand environmental influences on past environments, the modern physical, chemical and biological conditions of the loch and surrounding catchment were studied. Both observational and computer modelled annual inner basin salinity show a clear response to climatic forcing, modulated by NAO behaviour. Main basin salinity appears to remain very stable and a well-defined salinity: δ¹⁸O relationship suggests excellent potential for palaeotemperature reconstructions based on foraminiferal δ¹⁸O . Multi-variate statistical analyses identified 4 benthic foraminiferal assemblage groups in the surface sediments of the loch: A) restricted basin (E. scaber); B) very high current activity (C. lobatulus-A. mammilla -A. beccarii); C) calm environment undera stratified water column (B. marginata-N. turgida-S. fusiformis) and D) coastal water influence and mild/episodic current activity (A. beccarii-C. lobatulus-S. wrightii-E. excavatum). Using assemblage data, an existing benthic foraminiferal transfer function was modified in order to reconstruct Loch Sunart bottom water temperature (BWS); these reconstructions agree well with Scottish coastal temperature series (Millport). C. lobatulus appears to calcify close to theoretical equilibrium δ¹⁸O calcite (Δδ¹⁸O = -0.11 ± 0.17 %), probably during the warm bottom water temperatures (BWT) of late autumn, and predominantly reflects changes in BWT rather than BWS in the main basin of Loch Sunart. The first late Holocene high resolution palaeoenvironmental reconstruction from the deep (121 m) main basin of Loch Sunart is presented; gravity core (GC023) is 3 m long and spans the last 2,000 years. Despite difficulties with geochronology, palaeoenvironmental reconstructions from Loch Sunart suggest that these high resolution sedimentary archives have the potential to resolve inter-annual marine climate variability of the order of 1-2°C and capture an integrated record of changes in the catchment and marine environment

The evolution of a coastal carbon store over the last millennium

This work was financially supported by the Natural Environment Research Council (grant number: NE/L501852/1), the EU FPV HOLSMEER project (EVK2-CT-2000-00060) and the EU FPVI Millennium project (contract number 017008), Biotechnology and Biological Sciences Research Council (grant number: BB/M026620/1) with additional support from the NERC Radiocarbon Facility (Allocation 1154.1005 and 2195.1019).Fjord sediments are recognized as hotspots for the burial and storage of organic carbon, yet little is known about the long-term drivers of significant terrestrial organic carbon (OC) transfers into these coastal carbon stores. The mid-latitude fjord catchments of Scotland have a long history of human occupation and environmental disturbance. We provide new evidence to show that increased anthropogenic disturbances over the last 500 years appear to have driven a step change in the magnitude of terrestrial OC transported to the coastal ocean. Increased pressures from mining, agriculture and forestry over the latter half of the last millennium have destabilized catchment soils and remobilized deep stores of aged OC from the catchment to the coastal ocean. Here we show that fjord sediments are capable of acting as highly responsive and effective terrestrial OC sinks, with OC accumulation rates increasing up to 20 % during the peak period of anthropogenic disturbance. The responsiveness and magnitude of the fjord OC sink represents a potentially significant time-evolving component of the global carbon cycle that is currently not recognized but has the potential to become increasingly important in the understanding of the role of these coastal carbon stores in our climate system.PostprintPeer reviewe

Antiphased dust deposition and productivity in the Antarctic Zone over 1.5 million years

The Southern Ocean paleoceanography provides key insights into how iron fertilization and oceanic productivity developed through Pleistocene ice-ages and their role in influencing the carbon cycle. We report a high-resolution record of dust deposition and ocean productivity for the Antarctic Zone, close to the main dust source, Patagonia. Our deep-ocean records cover the last 1.5 Ma, thus doubling that from Antarctic ice-cores. We find a 5 to 15-fold increase in dust deposition during glacials and a 2 to 5-fold increase in biogenic silica deposition, reflecting higher ocean productivity during interglacials. This antiphasing persisted throughout the last 25 glacial cycles. Dust deposition became more pronounced across the Mid-Pleistocene Transition (MPT) in the Southern Hemisphere, with an abrupt shift suggesting more severe glaciations since ~0.9 Ma. Productivity was intermediate pre-MPT, lowest during the MPT and highest since 0.4 Ma. Generally, glacials experienced extended sea-ice cover, reduced bottom-water export and Weddell Gyre dynamics, which helped lower atmospheric CO2 levels

Palynology and micropalaeontology of the Pliocene - Pleistocene transition in outcrop from the western Caspian Sea, Azerbaijan : potential links with the Mediterranean, Black Sea and the Arctic Ocean?

New palynological, ostracod and foraminiferal data are presented from a long outcrop section in the Jeirankechmez river valley, Azerbaijan, near the western coast of the Caspian Sea. The interval studied includes the upper part of the Psliocene Productive Series and overlying Plio-Pleistocene Akchagylian (Akchagyl) and Apsheronian (Apsheron) regional stages. Productive Series sediments were deposited in a closed fluvio-lacustrine basin, isolated from any marine influence. The onset of Akchagyl deposition is marked by a lithological change associated with a significant flooding event that, at its maximum extent, reached the Sea of Azov and into present-day Iran, Kazakhstan, Turkmenistan and Russia. At the Jeirankechmez locality, the lowermost beds of the Akchagyl contain predominantly freshwater assemblages with very minimal marine or brackish content showing that the onset of Akchagyl deposition was not a marine induced event. Reworked Mesozoic palynomorphs occur frequently in this lowermost interval, including the reworked pollen taxa Aquilapollenites-Triprojectus that were eroded from the north or north-east. Significant marine influence is evident ca. 30 m above the base of the Akchagyl in the studied outcrop, marked by the ‘Cassidulina Beds’ which contain a distinct but low diversity assemblage of foraminifera that occurs widely and can be correlated in many parts of the greater Caspian region. Dinoflagellate cysts (dinocysts) in the marine interval include frequent specimens very similar to Algidasphaeridium capillatum (Matsuoka and Bujak), a species only previously recorded from the northern Bering Sea. The combined evidence from these dinocysts and foraminifera suggests that a marine (i.e. seaway) connection existed briefly between the Arctic Ocean and the Caspian Sea at the very end of the Pliocene. Re-examination of core material from the Adriatic Sea shows that Cassidulina reniforme (Nørvang) was present in the Mediterranean during and shortly after the Last Glacial Maximum. The possibility that the end Pliocene marine incursion came from the Mediterranean via the Black Sea region to the Caspian Sea cannot be entirely ruled out but is considered unlikely. Biometric analyses are applied to obtain a better understanding of the palaeoenvironmental significance of the assemblages dominated by cassidulinids. An interval > 300 m thick is assigned to the Apsheron regional stage on the basis of predominantly brackish ostracod and dinocyst associations. The dinocysts are of ‘Peri-Paratethyan’ affinity and closely resemble species first described from Miocene and Pliocene sediments in the Pannonian and Dacic basins of Eastern Europe. Many similarities exist in the microplankton records (dinocysts and acritarchs) between the Caspian Sea, the Black Sea and Central Paratethys.PostprintPeer reviewe

Antiphased dust deposition and productivity in the Antarctic Zone over 1.5 million years

The Southern Ocean paleoceanography provides key insights into how iron fertilization and oceanic productivity developed through Pleistocene ice-ages and their role in influencing the carbon cycle. We report a high-resolution record of dust deposition and ocean productivity for the Antarctic Zone, close to the main dust source, Patagonia. Our deep-ocean records cover the last 1.5 Ma, thus doubling that from Antarctic ice-cores. We find a 5 to 15-fold increase in dust deposition during glacials and a 2 to 5-fold increase in biogenic silica deposition, reflecting higher ocean productivity during interglacials. This antiphasing persisted throughout the last 25 glacial cycles. Dust deposition became more pronounced across the Mid-Pleistocene Transition (MPT) in the Southern Hemisphere, with an abrupt shift suggesting more severe glaciations since ~0.9 Ma. Productivity was intermediate pre-MPT, lowest during the MPT and highest since 0.4 Ma. Generally, glacials experienced extended sea-ice cover, reduced bottom-water export and Weddell Gyre dynamics, which helped lower atmospheric CO2 levels

Marine climate variability during the last millennium:The Loch Sunart record, Scotland, UK

The first decadal-scale reconstruction of British coastal temperature anomalies spanning the last millennium is presented from a sea loch (fjord) basin. Loch Sunart, NW Scotland. Based on modern observation and the results of previous numerical modeling of fjord circulation, benthic foraminiferal oxygen isotope records are interpreted as a record of summer temperature. A significant climate transition, apparently driven by large-scale reorganization of northern Hemisphere atmospheric circulation, occurs in the record around AD 1400. An abrupt, but relatively short-lived climate warming occurs between AD 1540-1610, when the bottom water temperature anomalies are 11 degrees C above the long-term average, which is warmer than most of the 20th century and the late Medieval Warm Period. A long-term cooling occurs throughout the Little Ice Age culminating in the coldest recorded temperature anomalies between the late 1920s and 1940s The warmest reconstructed temperatures of the past millennium occurred in the last 5 years of the record, which ends in 2006. A replicated post-AD 1900 shift in benthic foraminiferal delta C-13 of ca -0.6 parts per thousand provides evidence of the Oceanic delta C-13 Suess Effect; this feature provides an independent test of the age model and demonstrates the value of benthic foraminifera as palaeo-proxies in the Loch Sunart record (C) 2010 Elsevier Ltd. All rights reserved.</p

Identification of the Icelandic Landnam tephra (AD 871 +/- 2) in Scottish fjordic sediment

Certain marginal marine environments, such as the Scottish fjord systems, contain high-resolution records of palaeoclimatic change in which decadal to centennial climatic events can be resolved. This paper explores the possibilities of using tephrochronology to stratigraphically constrain the timing of such events in the Loch Sunart record (MD04-2831) on the NW coast of Scotland (UK). One tephra horizon (containing both silicic and basaltic shards) is identified within Late Holocene sediment with geochemical analyses of the basaltic shards suggesting an origin in the Veidiviitn-Baroarbunga volcanic system. Radiocarbon age estimates and stratigraphic information suggests that the AD 871 Landnam tephra is the most likely candidate. The shards identified within this horizon appear hydrated and indicate the operation of post-depositional weathering processes possibly influenced by the saline conditions of the fjord environment. (C) 2011 Elsevier Ltd and INQUA. All rights reserved.</p

Identification of the Icelandic Landnam tephra (AD 871 +/- 2) in Scottish fjordic sediment

Certain marginal marine environments, such as the Scottish fjord systems, contain high-resolution records of palaeoclimatic change in which decadal to centennial climatic events can be resolved. This paper explores the possibilities of using tephrochronology to stratigraphically constrain the timing of such events in the Loch Sunart record (MD04-2831) on the NW coast of Scotland (UK). One tephra horizon (containing both silicic and basaltic shards) is identified within Late Holocene sediment with geochemical analyses of the basaltic shards suggesting an origin in the Veidiviitn-Baroarbunga volcanic system. Radiocarbon age estimates and stratigraphic information suggests that the AD 871 Landnam tephra is the most likely candidate. The shards identified within this horizon appear hydrated and indicate the operation of post-depositional weathering processes possibly influenced by the saline conditions of the fjord environment. (C) 2011 Elsevier Ltd and INQUA. All rights reserved.</p