Abstract
Despite similar average global air temperatures and atmospheric greenhouse gas concentrations to the pre-industrial period, interglacial Marine Oxygen Isotope stage 11c (MIS 11c 395 – 425 ka) shows clear evidence of a significantly reduced Greenland Ice Sheet (GIS) compared to today. Furthermore, numerous records contain evidence for mid-interglacial abrupt climate changes in North Atlantic marine sediments and Northern European lake sediments. An identified isochronous tephra horizon recorded in lacustrine sediments at Marks
Tey which connects a cooling event (CE) in Eastern England and marine sediments at Ocean Drilling Programme (ODP) Site 980 (Northeast Atlantic) enables the investigation of concurrent changes in this region.
This thesis presents a decadal-scale isotopic reconstruction of air temperature changes in addition to targeted lipid biomarker analysis for examining local hydrology. Using six ocean sediment cores (ODP) Sites 980, 983, 984; and International Ocean Drilling Programme (IODP) Sites U1304, U1305, and U1302), surface ocean conditions in the subpolar North Atlantic and changes in the strength of Nordic Seas overflows throughout MIS 11c have been
reconstructed.
Decadal-scale air temperature changes from Marks Tey reveal a millennial-scale decline marked by multiple brief centennial-scale events, culminating in a centennial-scale vegetational response, coinciding with increased wildfire activity in the catchment.
North Atlantic reconstructions show two intervals of stronger Atlantic Meridional Overturning Circulation (AMOC)/faster overflows separated by a broad interval of AMOC weakening/declining overflows. The first phase (425 – 415 ka) is dominated by strong Denmark Strait Overflow Waters (DSOW), likely linked to remnant glacial icesheets. The second phase (411 – 407 ka) is dominated by strong Iceland Scotland Overflow Waters (ISOW), likely associated with the second July summer insolation peak (65⁰N). The period of declining AMOC/DSOW from 415 – 411 ka coincided with increasing GIS meltwater flux. The highest rates of meltwater flux (~ 0.1 Sverdrups; 1 Sv = 106m-3) coincided with the weakest ISOW and DSOW interval (overall AMOC reduction of ~ 50%) and the CE at Marks Tey. This suggests that GIS melt likely weakened deep water formation, AMOC, and triggered abrupt
circum-North Atlantic climate change.
Tey which connects a cooling event (CE) in Eastern England and marine sediments at Ocean Drilling Programme (ODP) Site 980 (Northeast Atlantic) enables the investigation of concurrent changes in this region.
This thesis presents a decadal-scale isotopic reconstruction of air temperature changes in addition to targeted lipid biomarker analysis for examining local hydrology. Using six ocean sediment cores (ODP) Sites 980, 983, 984; and International Ocean Drilling Programme (IODP) Sites U1304, U1305, and U1302), surface ocean conditions in the subpolar North Atlantic and changes in the strength of Nordic Seas overflows throughout MIS 11c have been
reconstructed.
Decadal-scale air temperature changes from Marks Tey reveal a millennial-scale decline marked by multiple brief centennial-scale events, culminating in a centennial-scale vegetational response, coinciding with increased wildfire activity in the catchment.
North Atlantic reconstructions show two intervals of stronger Atlantic Meridional Overturning Circulation (AMOC)/faster overflows separated by a broad interval of AMOC weakening/declining overflows. The first phase (425 – 415 ka) is dominated by strong Denmark Strait Overflow Waters (DSOW), likely linked to remnant glacial icesheets. The second phase (411 – 407 ka) is dominated by strong Iceland Scotland Overflow Waters (ISOW), likely associated with the second July summer insolation peak (65⁰N). The period of declining AMOC/DSOW from 415 – 411 ka coincided with increasing GIS meltwater flux. The highest rates of meltwater flux (~ 0.1 Sverdrups; 1 Sv = 106m-3) coincided with the weakest ISOW and DSOW interval (overall AMOC reduction of ~ 50%) and the CE at Marks Tey. This suggests that GIS melt likely weakened deep water formation, AMOC, and triggered abrupt
circum-North Atlantic climate change.
| Original language | English |
|---|---|
| Qualification | Ph.D. |
| Awarding Institution |
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| Supervisors/Advisors |
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| Award date | 1 Sept 2024 |
| Publication status | Unpublished - 2024 |
Keywords
- AMOC
- Ocean Circulation
- North Atlantic
- Quaternary
- Climate Change
- Nordic Seas Overflows
- MIS 11c
- Abrupt climate change
- sortable silt
- Greenland Ice Sheet
