During the 2015-2016 field investigation seasons the Rising Tides project has continued to make progress un-wrapping the story associated with the changes in sea-level around the mainland of Orkney. Two sites have been the focus of activity, namely the Bay of Firth and the Loch of Stenness.
Bay of Firth
Our previous research in the Bay of Firth has led to a complex model of flooding as relative sea-levels rose. Today the Bay contains two islands, interconnected to the mainland by a series of shallow rock ridges almost exposed at the lowest spring tides. Between each of the rock ridges a series of basins has been the focus of geophysical seismic profiling that revealed a deep sequence of sediments have been targeted for coring. The purpose of this was to understand the flooding history (you can read some of our previous work on this in “A Multi-disciplinary Approach to the Archaeological Investigation of a Bedrock-Dominated Shallow-Marine Landscape: an example from the Bay of Firth, Orkney, UK”, DOI: 10.1111/j.1095-9270.2012.00360.x, http://onlinelibrary.wiley.com/doi/10.1111/j.1095-9270.2012.00360.x/abstract). A number of peat layers were identified, together with key sequences, containing microfossils indicating where these basins once held fresh water lochs and the transition from fresh to marine conditions.
It is important for us to understand the sequence of sea-level rise here and its impact on the changing landscape of the bay in order to interpret various stone features that have been identified on the seafloor. During the investigation of one of these sites, a 40m diameter circular feature comprising upturned stones (image), we were joined by the BBC who were filming for a documentary series to be aired in Jan 2017 on the archaeology of Orkney, “Britain’s Ancient Capital: Secrets of Orkney” (Jan 2nd, BBC2, 9pm). The date at which individual features were flooded will help in our analysis of features like this. Read a review of the series by Caroline at http://oxbowdbbc.wordpress.com/2016/12/29/secrets-of-orkney/.
Loch of Stenness
The investigations here have focused mainly on the Loch of Stenness to the west of the Brodgar isthmus. The loch is a brackish loch connected to the sea through the narrow and shallow outlet at the Brig o Waith. In the summer of 2016 an attempt was also made to survey the loch of Harry however due to intense gas build-up in the sediments here this proved to be a difficult task. The landscape around the isthmus sets the scene for the iconic sites of the Ring of Brodgar, Stones of Stenness and Ness of Brodgar. The full findings of our work can be read in the recently published article in the Journal of Archaeological Sciences, “The environmental context of the Neolithic monuments on the Brodgar Isthmus, Mainland, Orkney” (DOI: 10.1016/j.jasrep.2016.05.032). Our work concludes that when construction began the isthmus was at least double the width and the lowered water levels in the Loch of Stenness exposed a 3km or more length of rocky shore that could have provided a handy construction material. Over time this was gradually drowned as water levels rose (see figure). Further, analysis of the sediment build-up in the loch revealed a ten-fold increase in the accumulation of sediment at the beginning of the Neolithic, interestingly, this is likely to be linked to changes in the surrounding landscape as tree cover was removed.
In 2017 we will continue the investigation of this landscape with a joint project with Orkney College where we will research the outlet of the loch into the Bay of Ireland. This is the location where a large oak log was discovered by Dr Ted Pollard in 2013 and various divers have reported submerged peats. The investigation will be run as a community project so there will be lots of opportunity for the public to be involved onland and through SeaSearch in the diving operations. Watch out for the first stage of this to be announced in local press in early March 2017.