Diatoms from the late Holocene of the western Chukchi Sea, Arctic Ocean: environmental signals and palaeoceanography

• Main Author: Browaldh, Erik
• Format: Bachelor Thesis
• Language: English
• Published: Stockholms universitet, Institutionen för geologiska vetenskaper 2022
• Subjects: diatoms; late holocene; SWERUS-L2-2-PC1; Herald Canyon; Chukchi Sea; ice-algae; sympagic; cryophilic; warm water diatom; Bering Sea Water species; bottom water temperature; BWT; benthic foraminifera; palaeothermometry; ice dynamics; Fragilariopsis; Fossula arctica; Paralia sulcata; Shionodiscus oestrupii; Thalassiosira simonsenii; Chaetoceros; Chaetoceros sp. 7; Geology; Geologi; Arctic; Arctic Ocean; Bering Sea; Gateway The; Pacific; Västra; Arktis*; Arktiska oceanen; Chukchi; Climate change; Foraminifera*; Global warming; ice algae; Sea ice
• Online Access: http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-208183

The sediment Core SWERUS-L2-2-PC1 (2PC) retrieved from the Chukchi Sea, Arctic Ocean sits in an oceanographically dynamic location at the Arctic-Pacific Ocean gateway. The 8.3 m-long core was retrieved in Herald Canyon at the marginal ice zone at 57 m depth. Core 2PC is well-positioned to record variability in inflow of Bering Sea Water (BSW) and Pacific Water (PW) in Herald Canyon. With the 2PC high sedimentation rate (200 cm/kyr), two independent age models (radiocarbon and palaeomagnetism) based on tephra age markers, and a richness in well-preserved siliceous sediment, validate 2PC as an outstanding sequence for applying diatom assemblage analysis as a proxy for ocean-climate change back to 4250 years BP, including the past few hundred years where global warming and sea ice decline is recorded by instrumental records. These characteristics make Core-2PC a useful record for investigating the role of PW on sea ice variability in the Chukchi Sea, both in the past and predicting the future. To investigate the impact of PW on ocean and sea ice conditions in the Chukchi Sea, diatom assemblage analysis was performed on 49 samples through the Late Holocene. The over-arching goal was to test the hypothesis, suggested by existing research on 2PC using benthic foraminifera Mg/Ca palaeothermometry, that the strength of PW inflow into the Chukchi Sea via Herald Canyon has varied on a time scales of ~500-1000 years in the past 4000 years. PW is slightly warmer than resident Arctic surface waters and is known to be an important control on Arctic sea-ice. The diatom assemblage approach assumes that there are recognizable differences between end-member diatom assemblages that are characteristic of PW versus Arctic Ocean type environments associated with extensive sea-ice conditions. The mapping of species in the Herald Canyon was used to test the idea of variability of sea-ice extent and the role of the Pacific Ocean forcings into the western Chukchi Sea. The results reveal diverse diatom assemblages throughout the past 4000 ...