Palynofacies analysis and organic-walled dinoflagellate cysts as indicators of palaeo-hydrographic changes: an example from Holocene sediments in Skálafjord, Faroe Islands

Abstract

This study documents Holocene variations in organic matter deposition from ca. 6350 cal yr BC to AD 1430 in Skálafjord, Faroe Islands, and uses this information to assess palaeo-hydrographic conditions. The chronology of the interval studied is based on five AMS 14C ages. Based on the total sedimentary organic content, the sediments dating to ca. 6350 cal yr BC to AD 160 have been deposited under dysoxic bottom water conditions suggesting good ventilation in the water column. The sediments dating to ca. AD 160–1090 have been deposited under decreasing oxygen availability; from AD 1090 to 1430, suboxic bottom water conditions characterised the fjord. High terrestrial influx characterised most sediments in the study interval; however, moderate terrestrial influx was recorded in sediments dating to ca. 6350–5670 cal yr BC. Based on the dinoflagellate cyst assemblages, changes in the nutrient availability were inferred in the waters of the fjord over the study period. The nutrients were minimal at ca. 6350–5670 cal yr BC; they increased in the interval ca. 5670–685 cal yr BC and became very abundant at ca. 685 cal yr BC to AD 1260. A decreasing trend in nutrient availability was inferred in sediments of age ca. AD 1260–1430. A qualitative approach was used for the reconstruction of Holocene sea-surface temperature conditions based on dinoflagellate cyst and acritarch assemblages. The estimated sea-surface parameters highlighted the Mid-Holocene final stage of the Climatic Optimum (ca. 6350–5300 cal yr BC), the Neo-glaciation period (ca. 5300 cal yr BC to AD 260), a general climatic amelioration during the period ca. AD 260–1090 and a cooling at ca. AD 1090–1260.