The overarching aim of the project was to generate and interpret the first millennial scale robustly calibrated annually resolved reconstruction of the N. Atlantic Ocean circulation. The project utilised the reconstruction along with modelling simulations to produce an estimate for the variability in the horizontal circulation of the N. Atlantic and Nordic Seas, and identify the associated driving mechanisms. The implications of these insights for AMOC variability was also explored.

The project addressed the following hypotheses:
Hypothesis 1. The geochemistry of bivalve chronologies allows us to quantitatively reconstruct Sea surface temperature and salinity (SST/SSS) variability within each of the major N. Atlantic oceanographic provinces (e.g. subtropical gyre, subpolar gyre and North Atlantic Current) at annual timescales across the last millennium;
Hypothesis 2. The quantitative and annually resolved SST/SSS reconstructions from these spatial provinces will allow the identification of the dominant components of N. Atlantic circulation change over the last millennium;
Hypothesis 3. The integration of these reconstructions with state-of-the-art numerical climate modelling will (i) robustly identify the key mechanisms and drivers of N. Atlantic circulation variability at annual to multi-decadal timescales during the last millennium and (ii) allow the identification of the relevant sentinels of future N. Atlantic circulation and climate change.

The project employed a data-modelling approach involving the use of multi-proxies, growth increment width and stable/radioisotope geochemical (d18O, d13C and 14C) proxies, derived from new and existing absolutely-dated millennial scale sclerochronologies together with the analysis of the preindustrial control and millennial simulations carried out for the CMIP5 project and undertaking novel simulations using the ocean component of the 3rd Hadley Centre General Environmental Model (HadGEM3).

Specific Project Objectives:
1) To construct a 1000 year Glycymeris glycymeris absolutely dated sclerochronology from the Tiree Passage, NW Scotland;
2) Derive the relative contribution of salinity and temperature of the ambient water to the stable isotopic content of the shell by comparison of modern samples with the Tiree Passage and local instrumental temperature and salinity observational series (e.g. Tiree Passage and Keppel Pier oceanographic moorings), and estimate uncertainty in these relationships for the pre-observational era from CMIP5 model control run analysis;
3) Reconstruct annually resolved SST/SSSs in the Tiree Passage sclerochronology for the past 1000 years using stable isotope geochemical (d18O, d13C) and growth increment width proxies;
4) Identify and compare the amplitude, rate and frequency of SST/SSS variability in the Tiree Passage with reconstructions from N. Iceland and the Gulf of Maine. These shell records will further be compared with palaeoclimate reconstructions derived from coralline algal, ice cores, speleothems, dendrochronologies and lower resolution ocean sediment archives providing a comprehensive network of archives across the N. Atlantic region spanning the last several hundred to 1000 years;
5) Identify the timescale-dependant relationship between study site temperature and salinity (and therefore change in d18O) and the dominant components of N. Atlantic circulation, within the preindustrial control simulations of CMIP5;
6) Reconstruct the evolution of the above-identified N. Atlantic circulation components over the last 1000 years, and compare with results from the CMIP5 Millennial simulations and mechanisms in control simulations.
7) Quantify the relative impacts of ocean density changes and variations in wind stress forcing on the d18O variability observed at the proxy sites.
8) Quantify the impact of Maunder Minimum solar ultraviolet irradiance on N. Atlantic ocean-atmosphere