Cenozoic global ice-volume and temperature simulations with 1-D ice-sheet models forced by benthic δ¹⁸O records

Abstract

Variations in global ice volume and temperature over the Cenozoic era have been investigated with a set of one-dimensional (1-D) ice-sheet models. Simulations include three ice sheets representing glaciation in the Northern Hemisphere, i.e. in Eurasia, North America and Greenland, and two separate ice sheets for Antarctic glaciation. The continental mean Northern Hemisphere surface-air temperature has been derived through an inverse procedure from observed benthic δ18O records. These data have yielded a mutually consistent and continuous record of temperature, global ice volume and benthic δ18O over the past 35 Ma. The simple 1-D model shows good agreement with a comprehensive 3-D ice-sheet model for the past 3 Ma. On average, differences are only 1.0˚C for temperature and 6.2 m for sea level. Most notably, over the 35 Ma period, the reconstructed ice volume–temperature sensitivity shows a transition from a climate controlled by Southern Hemisphere ice sheets to one controlled by Northern Hemisphere ice sheets. Although the transient behaviour is important, equilibrium experiments show that the relationship between temperature and sea level is linear and symmetric, providing limited evidence for hysteresis. Furthermore, the results show a good comparison with other simulations of Antarctic ice volume and observed sea level.

Relationship between sea level and climate forcing by CO 2 on geological timescales

“…This study directly determines the relationship between CO 2 and sea level from data covering the entire range of climates experienced by the Earth over the past 40 My. We find a strong similarity to nonlinear relationships that have been proposed by ice-sheet modeling (37,38), theoretical studies (39), and a recent synthesis of deep-sea temperature and sea level for the past 10-40 My (40). A comparison between our work and these earlier studies is shown in Fig.…”

“…2, come from three methods: (i) gas bubbles trapped in ice cores [0-550 kya (6-8)]; (ii) the carbon isotopic composition of sedimentary alkenones recovered from deep-sea sediments-the fractionation between alkenones and total dissolved carbon in seawater is largely a function of [CO 2 ] aq [20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38]]; and (iii) the boron isotopic composition of planktic foraminifera from deepsea sediments, which depends on pH (e.g., ref. 14), from which [CO 2 ] aq and atmospheric CO 2 can be calculated [11][12][13][14][15][16][17][33][34][35][36]].…”

Evolution of the early Antarctic ice ages

“…To better understand the significance of the documented δ 18 O variability on long-term change in the high-latitude climate system, we make a conservative estimate of the minimum contribution of continental ice volume to the Site 1264 benthic at Site 1264 were never colder than the current temperature of 2.5°C and applying an average δ 18 O composition of OligoMiocene ice sheets (δ 18 O ice ) of −42‰ Vienna standard mean ocean water (VSMOW) (SI Methods) (16). These minimum ice volume estimates (Fig.…”

“…Here we analyze a new high-resolution deep-sea oxygen isotope (δ 18 O) record from the South Atlantic Ocean spanning an interval between 30.1 My and 17.1 My ago. The record displays major oscillations in deep-sea temperature and Antarctic ice volume in response to the ∼110-ky eccentricity modulation of precession.…”

Differences between the last two glacial maxima and implications for ice-sheet, δ18O, and sea-level reconstructions

“…First, temporal changes in the radiative balance of climate are important because ice masses have high albedo and reflect incoming solar radiation (e.g., Hansen et al, 2007Hansen et al, , 2008K€ ohler et al, 2010, 2015Rohling et al, 2012;PALAEOSENS project members, 2012;Martínez-Botí et al, 2015;Friedrich et al, 2016). Second, temporal development of ice-age cycles provides critical information about the nature of long-term climate cooling over the past few million years, in response to CO 2 reduction and interactions among ice, land cover, and climate (e.g., Clark et al, 2006;K€ ohler and Bintanja, 2008;de Boer et al, 2010de Boer et al, , 2012Hansen et al, 2013). Third, variable amplitude of individual ice ages helps to determine the relationship between climate change, astronomical climate forcing cycles, and climate feedbacks on timescales of 10se100s of kiloyears (e.g., Oglesby, 1990;Imbrie et al, 1993;Raymo et al, 2006;Colleoni et al, 2011Colleoni et al, , 2016Ganopolski and Calov, 2011;Carlson and Winsor, 2012;Abe-Ouchi et al, 2013;Hatfield et al, 2016;Liakka et al, 2016).…”