Abstract Iceberg discharges into the North Atlantic are important sources of fresh water, and the sediments they deposit can provide constraints on which sectors of different ice sheets were contributing icebergs. 40 Ar/ 39 Ar ages of sand-sized hornblende grains provide useful constraints on IRD (ice-rafted detritus) source areas. Heinrich events are intervals of anomalously high percentages of IRD in marine sediment cores of the North Atlantic IRD belt. In contrast to the others, Heinrich event 3 (H3) records a significantly lower flux of IRD. This study compares 40 Ar/ 39 Ar hornblende age distributions from the interval around and including H3 in giant gravity core EW9303-GGC31 from Orphan Knoll, in the southern part of the Labrador Sea, with piston core V28-82 in the eastern part of the North Atlantic IRD belt. Collectively, these results confirm that H3 represents a Hudson Strait IRD event, but that it was smaller than during H1, H2, H4 and H5, and therefore comprises only a small fraction of the detritus at the eastern North Atlantic location of V28-82. These results support a previously published interpretation of across-strait ice flow during H3 at Hudson Strait. Supplementary material: Appendix 1 is 40 Ar/ 39 Ar data from core EW9303-GGC31; Appendix 2 is grain counts across H3 from core V28-82; Appendix 3 is 40 Ar/ 39 Ar data from core V28-82; these are available at http://www.geolsoc.org.uk/SUP18631 .

The late glacial and deglacial history of the Southeastern Laurentide Ice Sheet involves the southward advance and subsequent northward retreat from southeastern Canada and the northeastern United States. Superposed on this advance and retreat are three major ice-rafting events associated with Heinrich events 2 and 1 (H2 and H1) and the Younger Dryas. Nd, Sr, and Pb isotopes were measured on the 63–150 μm, de-carbonated marine sediment for the period 24–10.5 14 C ka, from marine sediment core EW9303-GGC31, collected from the top of Orphan Knoll, a topographic high 550 km northeast of Newfoundland, Canada. In general, one of the problems with understanding ice-rafting records is the disparate provenance strategies that have been used in different studies. Nd and Sr isotopes have been widely used in the study of North Atlantic sediment provenance, and Pb isotopes and 40 Ar/ 39 Ar hornblende ages have also been used for provenance assessment in a number of studies. The new Nd, Sr, and Pb isotope data presented here are complementary to the published hornblende data from the same samples, and provide a data set that allows more confident comparison of this record with other published provenance studies. The results are consistent with reconstructions based on a combination of marine and land-based geomorphic observations.

A ~220,000-year record recovered in a 120-m-long sediment core from Bear Lake, Utah and Idaho, provides an opportunity to reconstruct climate change in the Great Basin and compare it with global climate records. Paleomagnetic data exhibit a geomagnetic feature that possibly occurred during the Laschamp excursion (ca. 40 ka). Although the feature does not exhibit excursional behavior (≥40° departure from the expected value), it might provide an additional age constraint for the sequence. Temporal changes in salinity, which are likely related to changes in freshwater input (mainly through the Bear River) or evaporation, are indicated by variations in mineral magnetic properties. These changes are represented by intervals with preserved detrital Fe-oxide minerals and with varying degrees of diagenetic alteration, including sulfidization. On the basis of these changes, the Bear Lake sequence is divided into seven mineral magnetic zones. The differing magnetic mineralogies among these zones reflect changes in deposition, preservation, and formation of magnetic phases related to factors such as lake level, river input, and water chemistry. The occurrence of greigite and pyrite in the lake sediments corresponds to periods of higher salinity. Pyrite is most abundant in intervals of highest salinity, suggesting that the extent of sulfidization is limited by the availability of SO 4 2‒ . During MIS 2 (zone II), Bear Lake transgressed to capture the Bear River, resulting in deposition of glacially derived hematite-rich detritus from the Uinta Mountains. Millennial-scale variations in the hematite content of Bear Lake sediments during the last glacial maximum (zone II) resemble Dansgaard-Oeschger (D-O) oscillations and Heinrich events (within dating uncertainties), suggesting that the influence of millennial-scale climate oscillations can extend beyond the North Atlantic and influence climate of the Great Basin. The magnetic mineralogy of zones IV–VII (MIS 5, 6, and 7) indicates varying degrees of post-depositional alteration between cold and warm substages, with greigite forming in fresher conditions and pyrite in the more saline conditions.

The surface of Mars preserves landforms associated with the largest known water floods. While most of these megafloods occurred more than 1 Ga ago, recent spacecraft images document a phase of outburst flooding and associated volcanism that seems no older than tens of millions of years. The megafloods that formed the Martian outflow channels had maximum discharges comparable to those of Earth’s ocean currents and its thermohaline circulation. On both Earth and Mars, abrupt and episodic operations of these megascale processes have been major factors in global climatic change. On relatively short time scales, by their influence on oceanic circulation, Earth’s Pleistocene megafloods probably (1) induced the Younger Dryas cooling of 12.8 ka ago, and (2) initiated the Bond cycles of ocean-climate oscillation with their associated Heinrich events of “iceberg armadas” into the North Atlantic. The Martian megafloods are hypothesized to have induced the episodic formation of a northern plains “ocean,” which, with contemporaneous volcanism, led to relatively brief periods of enhanced hydrological cycling on the land surface (the “MEGAOUTFLO Hypothesis”). This process of episodic short-duration climate change on Mars, operating at intervals of hundreds of millions of years, has parallels in the Neoproterozoic glaciation of Earth (the “Snowball Earth Hypothesis”). Both phenomena are theorized to involve abrupt and spectacular planet-wide climate oscillations, and associated feedbacks with ocean circulation, land-surface weathering, glaciation, and atmospheric carbon dioxide. The critical factors for megascale environmental change on both Mars and Earth seem to be associated tectonics and volcanism, plus the abundance of water for planetary cycling. Some of the most important events in planetary history, including those of the biosphere, seem to be tied to cataclysmic episodes of massive hydrological change.