Modelling the freshwater cycle of the Arctic Ocean and North Atlantic during the Holocene

• Main Author: Davies, Frazer John
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: 2021
• Subjects: Arctic Ocean; freshwater; Holocene; climate change; climate modelling; Arctic; Climate change; Ice; north atlantic current; North Atlantic; permafrost; Sea ice
• Online Access: https://research.vu.nl/en/publications/1a1fa0f4-a266-4c50-98d2-edc976620e1b; http://hdl.handle.net/1871.1/1a1fa0f4-a266-4c50-98d2-edc976620e1b; https://research.vu.nl/ws/files/122388628/F%20J%20%20Davies%20-%20thesis.pdf; https://research.vu.nl/ws/files/122388630/F%20J%20%20Davies%20-%20cover.pdf; https://research.vu.nl/ws/files/122388632/F%20J%20%20Davies%20-%20title_page.pdf

The Arctic is at the forefront of climate change, given that it is warming at a rate faster than elsewhere on the planet and because the impacts of this warming extend much further than the Arctic region itself. Thus, the Arctic region has rightfully attracted a great deal of research interest that is geared towards understanding what has happened, what is happening and what is going to happen in the Arctic region and further afield in the 21st century and beyond. One issue researchers face is trying to understand the context of the current changes we are observing. For example, is an observed freshening of the Arctic Ocean due to melting glaciers and sea-ice, thawing permafrost, increased rainfall, a result of anthropogenic climate change we are observing, or is it part of a natural low-frequency cycle and how much can be accredited to anthropogenic forcings and how much is due to natural forcings. These are questions that I have grappled with within this thesis and I have presented here before you. To be able to do so I have employed the use of a climate model, called LOVECLIM. A climate model is a mathematical representation of the Earth’s atmosphere, oceans, land and vegetation. While such models do have their limitations, they are an essential part of climate studies when investigating mechanisms of the climate for which we have either limited observed data or reconstructed, proxy, data. In Chapter 2 I looked at “The Arctic Freshwater Hydrological Cycle during a naturally and an anthropogenically induced warm climate” focuses on comparing the climate simulations of two periods, the mid-Holocene (approximately 6ka BP) and one in the future, the 21st century, and the response of the Arctic Freshwater Hydrological Cycle. In Chapter 3 I looked at “The driving mechanisms of multicentennial variability of the Arctic Ocean freshwater content with the LOVECLIM climate model”. This revealed a peak periodicity at 165-years, with 95% significance, of the Arctic Ocean Freshwater content. Further analysis revealed that this intrinsic variability is driven by the low-frequency modulation of the heat and saline fluxes entering the Arctic Ocean, via the Barents and Kara Seas, via the North Atlantic Current. The next step was to see if this mechanism held up in a more realistic transient simulation. Therefore, in Chapter 4 “Simulating the Multicentennial variability of the Arctic Ocean freshwater content over the Holocene with the LOVECLIM climate model” was geared towards that task. In this chapter we performed a Holocene run, from 8ka to 0ka with the relevant orbital parameters and greenhouse gas concentrations. The transient simulation revealed a peak periodicity of 220-years, with 95% significance. The mechanisms driving this periodicity were the same as in Chapter 3 and when statistically analysed the robustness of the results from Chapter 3 were verified. Overall, the results of Chapters 3&4 showed that the Arctic Ocean possess an intrinsic low-frequency mode of variability and they both highlight the need for low-frequency mechanisms within the Artic Ocean, and from elsewhere, to be incorporated into discussions on the causes of the climate variability we are currently observing. Chapter 5 “The impact of Sahara desertification on Arctic cooling during the Holocene” does not directly follow on from the previous chapters, however it expands on the point I make in the previous paragraph, which calls for alternative mechanisms to be included within the causes of the current climate debate. In this chapter our results showed that through a long-range land-atmosphere teleconnection, the desertification of the Sahara in the mid-Holocene accounts for anywhere between 17 and 40% of the observed Arctic cooling between 9k and 0ka.