ALBERT

Description: The oceans of the early Cambrian (~541 to 509 million years ago) were the setting for a marked diversification of animal life. However, sea temperatures—a key component of the early Cambrian marine environment—remain unconstrained, in part because of a substantial time gap in the stable oxygen isotope ( 18 O) record before the evolution of euconodonts. We show that previously overlooked sources of fossil biogenic phosphate have the potential to fill this gap. Pristine phosphatic microfossils from the Comley Limestones, UK, yield a robust 18 O signature, suggesting sea surface temperatures of 20° to 25°C at high southern paleolatitudes (~65°S to 70°S) between ~514 and 509 million years ago. These sea temperatures are consistent with the distribution of coeval evaporite and calcrete deposits, peak continental weathering rates, and also our climate model simulations for this interval. Our results support an early Cambrian greenhouse climate comparable to those of the late Mesozoic and early Cenozoic, offering a framework for exploring the interplay between biotic and environmental controls on Cambrian animal diversification.

Description: Palaeoceanography relies on the assumption that parameters measureable in sediment cores correlate reliably to hydrographic parameters. Areas of dynamic watermass mixing, which generally have steep hydrographic gradients, therefore provide both a tempting target (large spatial and temporal differences in temperature and salinity) and a significant challenge (high flow velocities and high “noise”) for palaeoceanographers. Here, we investigate the ability of parameters measured on core tops to be used as the basis for simulating regional hydrography within one globally important area of watermass mixing, the Gulf of Cadiz. Using grainsize, sediment composition, benthic foraminiferal assemblage and benthic foraminiferal stable isotope analysis it is possible to build an effective framework for qualitative constraint of the position of the modern Mediterranean Outflow Water (MW) Plume. We propose that the Gulf of Cadiz slope can be sub-divided into 8 hydrographic zones reflecting these parameters; Proximal MW, Core MW1 (steep slopes), Core MW1 (gentle slopes), Distal MW1, Distal MW2, Lower Limit of MW plume, North Atlantic Deep Water and Ambient Atlantic Water. We anticipate that compilation of time-slice data will reveal hydrographic sub-divisions of the slope for the past in a similar manner, improving our understanding of past changes in the size and position of the MW plume, but more work needs to be done before a secure protocol for quantitative reconstruction can be created. Stable isotope analysis alone is insufficient for the task, with δ13C behaving in a non-conservative manner and δ18Ocalcite acting in an ambiguous way due to the competing influences of δ18Owater and temperature. It is likely that if a single parameter that unambiguously determines the difference between Mediterranean Water and Atlantic Water can be identified, combination with δ18Ocalcite will allow extension of our qualitative analysis into a quantitative means of palaeohydrographic reconstruction for this region. Similar complexity to that found in this study would be expected in any mixing region, and in particular on the majority of sediment drifts. We recommend that core top surveys similar to this study are performed on these sediment drift systems before any form of quantitative palaeohydrology is attempted.

Description: Highlights: • NW Pacific ice-rafted debris found further south than previously thought. • Largest iceberg events were comparable in magnitude to N Atlantic Heinrich Events. • Iceberg flux to ODP Site 1207 was episodic throughout the late Quaternary. • Kamchatka-Koryak bergs frequently reached south of the N Pacific Subarctic Front. • Ice-rafting and climate contrast sharply between the last two glacial periods. Abstract: The ice-rafted-debris (IRD) record of the open Northwest Pacific points towards the existence of substantial glacial ice on the Northeast Siberian coast during the late Quaternary. However, the scale and timing of glaciation and de-glaciation remains controversial due to the dearth of both onshore and offshore records. Existing IRD data suggests at least one event of dynamic and abrupt change during mid-late Marine Isotope Stage (MIS 3) which mimics the massive collapse of the Laurentide ice sheet during Heinrich Events. It is uncertain whether other events of this magnitude occurred during the late Quaternary. Here we present a ∼160,000 yr IRD series, planktic foraminiferal counts and an age model, derived from a benthic O curve, radiocarbon dates and tephrochronology, from core ODP 1207A (37.79°N, 162.75°E), revealing the presence of low but episodic flux of IRD. We conclude that glacial Northwest Pacific icebergs spread further south than previously thought, with icebergs emanating from Northeast Siberia being transported to the transition region between the subpolar and subtropical waters, south of the subarctic front during at least the Quaternary's last two glacial periods. The episodic nature of the 1207A IRD record during the last glacial, combined with coupled climate-iceberg modelling, suggests occasional times of much enhanced ice flux from the Kamchatka-Koryak coast, with other potential sources on the Sea of Okhotsk coast. These findings support the hypothesis of a variable but extensive ice mass during the last glacial over Northeast Siberia, particularly early in the last glacial period, behaving independently of North American and Eurasian ice masses. In strong contrast, IRD was absent during much of the penultimate glacial Marine Isotope Stage (MIS) 6 suggesting the possibility of very different Northeast Siberian ice coverage between the last two glacial periods.