Magmatism and glacial cycles: coupled oscillations?

• Main Author: Burley, J
• Other Authors: Katz, R, Ballentine, C, Battisti, D
• Format: Thesis
• Language: English
• Published: 2018
• Subjects: Earth sciences; Ice Sheet
• Online Access: https://ora.ox.ac.uk/objects/uuid:c55a6d98-d222-46de-8500-1ad44d05be75

The Earth's climate system is driven by varying insolation from the Sun. The dominant variations in insolation are at 23 and 40 thousand year periods, yet for the past million years the Earth’s climate has glacial cycles at approximately 100 kyr periodicity. These cycles are a coupled variation in temperature, ice volume, and atmospheric CO2. Somehow the Earth system’s collective response to 23 and 40 kyr insolation forcing produces 100 kyr glacial–interglacial cycles. Generally it has been assumed that the causative mechanisms are a combination of ice dynamics (high ice reflectivity controlling temperature) and ocean circulation (changing carbon partitioning between the deep ocean and the atmosphere, and heat transport to the poles). However, these proposed mechanisms have not yet resulted in a compelling theory for all three variations, particularly CO2. This thesis explores the role of volcanic CO2 emissions in glacial cycles. I calculate that glacial-driven sea level change alters the pressure on mid-ocean ridges (MORs), changing their CO2 emissions by approximately 10%. This occurs because pressure affects the thermodynamics of melt generation. The delay between sea level change and the consequent change in MOR CO2 emissions is several tens-of-thousands-of-years, conceptually consistent with a coupled non-linear oscillation that could disrupt glacial cycles from a 40 kyr mode to a multiple of that period. I develop an Earth system model to investigate this possibility, running for approximately one million years and explicitly calculating global temperatures, ice sheet configuration, and CO2 concentration in the atmosphere. The model is driven by insolation, with all other components varying in response (and according to their own interactions). This model calculates that volcanism is capable of causing a transition to ˜100 kyr glacial cycles, however the required average volcanic CO2 emissions are barely within the 95% confidence interval. Therefore it is possible for volcanic systems and glacial cycles to ...