The Last Interglacial (LIG) stage (ca. 130-115 ka), with polar temperatures likely 3-5 • C warmer than today, serves as a partial analogue for low-end future warming scenarios. Multiple indicators suggest that LIG global sea level (GSL) was higher than at present; based upon a small set of local sea level indicators, the Intergovernmental Panel on Climate Change (IPCC)'s Fourth Assessment Report inferred an elevation of approximately 4-6 m. While this estimate may be correct, it is based upon overly simplistic assumptions about the relationship between local sea level and global sea level. Sea level is often viewed as a simple function of changing global ice volume. This perspective neglects local variability, which arises from several factors, including the distortion of the geoid and the elastic and isostatic deformation of the solid Earth by shifting ice masses. Accurate reconstruction of past global and local sea levels, as well as ice sheet volumes, therefore requires integrating globally distributed data sets of local sea level indicators. To assess the robustness of the IPCC's global estimate and search for patterns in local sea level that are diagnostic of meltwater sources, we have compiled a comprehensive database that includes a variety of local sea level indicators from 47 localities, as well as a global sea level record derived from oxygen isotopes. We generate a global synthesis from these data using a novel statistical approach that couples Gaussian process regression to Markov Chain Monte Carlo simulation of geochronological errors. Our analysis strongly supports the hypothesis that global sea level during the Last Interglacial was higher than today, probably peaking between 6-9 m above the present level. This level is close to that expected from the complete melting of the Greenland Ice Sheet, or from major melting of both the Greenland and West Antarctic Ice Sheets. In the period when sea level was within 10 m of the modern value, the fastest rate of sea level rise sustained for a 1 ky period was likely about 80-110 cm per century. Combined with the evidence for mildly higher temperatures during the LIG, our results highlight the vulnerability of ice sheets to even relatively low levels of sustained global warming.

Glacial deposits of Sturtian and Marinoan age occur in the well-studied Neoproterozoic successions of northern Namibia, South Australia, and northwestern Canada. In all three regions, the Marinoan glaciation is presaged by a large negative δ 13 C anomaly, and the cap carbonates to both glacial units share a suite of unique sedimentological, stratigraphic, and geochemical features. These global chronostratigraphic markers are the bases of a new correlation scheme for the Neoproterozoic that corroborates radiometric data that indicate that there were three glacial epochs between ca. 750 and 580 Ma. Intraregional correlation of Neoproterozoic successions in the present-day North Atlantic region suggests that glacial diamictite pairs in the Polarisbreen Group in northeastern Svalbard and the Tillite Group in eastern Greenland were deposited during the Marinoan glaciation, whereas the younger of a pair of glacials (Mortensnes Formation) in the Vestertana Group of northern Norway was deposited during the third (Gaskiers) Neoproterozoic glaciation. Gaskiers-aged glacial deposits are neither globally distributed nor overlain by a widespread cap carbonate but are associated with an extremely negative δ 13 C anomaly. The chronology developed here provides the framework for a new, high-resolution model carbon-isotope record for the Neoproterozoic comprising new δ 13 C (carbonate) data from Svalbard (Akademikerbreen Group) and Namibia (Otavi Group) and data in the literature from Svalbard, Namibia, and Oman. A new U-Pb zircon age of 760 ± 1 Ma from an ash bed in the Ombombo Subgroup in Namibia provides the oldest direct time-calibration point in the compilation, but the time scale of this preliminary δ 13 C record remains poorly constrained.

We describe an ultra-sensitive atomic magnetometer using optically-pumped potassium atoms operating in spin-exchange relaxation free (SERF) regime. We demonstrate magnetic field sensitivity of 160 aT/Hz 1/2 in a gradiometer arrangement with a measurement volume of 0.45 cm 3 and energy resolution per unit time of 44h. As an example of a new application enabled by such a magnetometer we describe measurements of weak remnant rock magnetization as a function of temperature with a sensitivity on the order of 10 −10 emu/cm 3 /Hz 1/2 and temperatures up to 420 • C.High sensitivity magnetometery is used in many fields of science, including physics, biology, neuroscience, materials science and geology. Traditionally low-temperature SQUID magnetometers have been used for most demanding applications, but recent development of atomic magnetometers with sub-femtotesla sensitivity has opened new possibilities for ultra-sensitive magnetometery [1].Here we report new results of sensitive magnetic field measurements using a spin-exchange relaxation-free potassium magnetometer. By eliminating several sources of ambient magnetic field noise and optimizing operation of the magnetometer we achieve magnetic field sensitivity of 160 aT/Hz 1/2 at 40 Hz. The measurement volume used to obtain this sensitivity is 0.45 cm 3 , resulting in a magnetic field energy resolution of V B 2 /2µ 0 = 44h, a factor of 10 smaller than previously achieved with atomic magnetometers [2]. Energy resolution on the order ofh has been realized with SQUIDs at high frequency and milli-Kelvin temperatures with small input coils [3,4]. However for cm-sized SQUID sensors operating at 4.2 K the energy resolution at low frequency is typically several hundredsh [5,6,7] and the magnetic field sensitivity is about 1 fT/Hz 1/2 [8].When comparing various magnetometery techniques it is important to distinguish between applications requiring detection of smallest magnetic moments and those requiring detection of smallest magnetizations. For the former, it is usually advantageous to use the smallest possible sensor. For example, magnetic resonance force microscopy (MRFM) can detect a single electron spin [9]. On the other hand, for detection of very weak magnetization one needs a sensor with the highest magnetic field sensitivity, since B ∼ µ 0 M in the vicinity of the source. For example, recently developed magnetometers using a single nitrogen-vacancy (NV) center in diamond are promising for detection of single electron and nuclear spins because of their small size [10,11]. In diamond crystals with larger concentration of NV centers the magnetic field sensitivity is limited by dipolar interactions with other inactive color centers and has been optimistically projected at 10 −16 T/Hz 1/2 /cm 3/2 [12], which is the level already realized experimentally in this work.One of the well-developed magnetometry applications requiring high magnetization sensitivity is paleomagnetism [13]. Analysis of magnitude and direction of remnant magnetization in ancient rocks provides geologica...

The Neoproterozoic was an era of great environmental and biological change, but a paucity of direct and precise age constraints on strata from this time has prevented the complete integration of these records. We present four high-precision U-Pb ages for Neoproterozoic rocks in northwestern Canada that constrain large perturbations in the carbon cycle, a major diversification and depletion in the microfossil record, and the onset of the Sturtian glaciation. A volcanic tuff interbedded with Sturtian glacial deposits, dated at 716.5 million years ago, is synchronous with the age of the Franklin large igneous province and paleomagnetic poles that pin Laurentia to an equatorial position. Ice was therefore grounded below sea level at very low paleolatitudes, which implies that the Sturtian glaciation was global in extent.