P. Graham Mortyn

Biological response to millennial variability of dust and nutrient supply in the Subantarctic South Atlantic Ocean.

Fluxes of lithogenic material and fluxes of three palaeo-productivity proxies (organic carbon, biogenic opal and alkenones) over the past 100 000 years were determined using the 230Th-normalization method in three sediment cores from the Subantarctic South Atlantic Ocean. Features in the lithogenic flux record of each core correspond to similar features in the record of dust deposition in the EPICA Dome C ice core. Biogenic fluxes correlate with lithogenic fluxes in each sediment core. Our preferred interpretation is that South American dust, most probably from Patagonia, constitutes a major source of lithogenic material in Subantarctic South Atlantic sediments, and that past biological productivity in this region responded to variability in the supply of dust, probably due to biologically available iron carried by the dust. Greater nutrient supply as well as greater nutrient utilization (stimulated by dust) contributed to Subantarctic productivity during cold periods, in contrast to the region south of the Antarctic Polar Front (APF), where reduced nutrient supply during cold periods was the principal factor limiting productivity. The anti-phased patterns of productivity on opposite sides of the APF point to shifts in the physical supply of nutrients and to dust as cofactors regulating productivity in the Southern Ocean.

A global multiproxy database for temperature reconstructions of the Common Era

Reproducible climate reconstructions of the Common Era (1 CE to present) are key to placing industrial-era warming into the context of natural climatic variability. Here we present a community-sourced database of temperature-sensitive proxy records from the PAGES2k initiative. The database gathers 692 records from 648 locations, including all continental regions and major ocean basins. The records are from trees, ice, sediment, corals, speleothems, documentary evidence, and other archives. They range in length from 50 to 2000 years, with a median of 547 years, while temporal resolution ranges from biweekly to centennial. Nearly half of the proxy time series are significantly correlated with HadCRUT4.2 surface temperature over the period 1850–2014. Global temperature composites show a remarkable degree of coherence between high- and low-resolution archives, with broadly similar patterns across archive types, terrestrial versus marine locations, and screening criteria. The database is suited to investigations of global and regional temperature variability over the Common Era, and is shared in the Linked Paleo Data (LiPD) format, including serializations in Matlab, R and Python.

Field-based validation of a diagenetic effect on G. ruber Mg/Ca paleothermometry: Core top results from the Aegean Sea (eastern Mediterranean)

Recent work across the Mediterranean Sea has illustrated the salinity and overgrowth effects on planktonic foraminiferal Mg/Ca, which potentially confound the use of this as a temperature proxy for paleoceanographic reconstructions. To test and verify these effects, we present new Aegean Sea results which reveal Mg/Ca values that were unreasonably high to be explained by temperature or salinity variations alone, confirming that foraminiferal Mg/Ca is affected by diagenesis. We have specifically targeted Globigerinoides ruber (w, sensu stricto), from a series of modern core tops spanning a strong sea surface salinity gradient and a minor sea surface temperature range, along a north-south Aegean Sea transect. Scanning Electron Microscopy analyses show that G. ruber specimens were covered by microscale euhedral crystallites of inorganic precipitates. This secondary calcite phase seems to be responsible for the anomalously high Mg/Ca ratios and likely formed near the sediment/water interface from CaCO3 supersaturated interstitial seawater. We also have clear evidence of diagenetic alteration in a north-south direction along the Aegean Sea, possibly depending on salinity and calcite saturation state gradients. These observations illustrate the necessity of alternative techniques (e.g., flow-through time resolved analysis or laser ablation inductively coupled plasma mass spectrometry) to potentially overcome these diagenetic issues and develop a more reliable and sensitive temperature proxy in similar subtropical settings characterized by high salinity, excessive evaporation, and restricted circulation.

Mediterranean circulation perturbations over the last five centuries: Relevance to past Eastern Mediterranean Transient-type events

The Eastern Mediterranean Transient (EMT) occurred in the Aegean Sea from 1988 to 1995 and is the most significant intermediate-to-deep Mediterranean overturning perturbation reported by instrumental records. The EMT was likely caused by accumulation of high salinity waters in the Levantine and enhanced heat loss in the Aegean Sea, coupled with surface water freshening in the Sicily Channel. It is still unknown whether similar transients occurred in the past and, if so, what their forcing processes were. In this study, sediments from the Sicily Channel document surface water freshening (SCFR) at 1910 ± 12, 1812 ± 18, 1725 ± 25 and 1580 ± 30 CE. A regional ocean hindcast links SCFR to enhanced deep-water production and in turn to strengthened Mediterranean thermohaline circulation. Independent evidence collected in the Aegean Sea supports this reconstruction, showing that enhanced bottom water ventilation in the Eastern Mediterranean was associated with each SCFR event. Comparison between the records and multi-decadal atmospheric circulation patterns and climatic external forcings indicates that Mediterranean circulation destabilisation occurs during positive North Atlantic Oscillation (NAO) and negative Atlantic Multidecadal Oscillation (AMO) phases, reduced solar activity and strong tropical volcanic eruptions. They may have recurrently produced favourable deep-water formation conditions, both increasing salinity and reducing temperature on multi-decadal time scales.

Late Quaternary palaeoenvironmental reconstruction of sediment drift accumulation in the Malta Graben (central Mediterranean Sea)

The Malta Graben is a deep tectonic depression in the Sicily Channel, bounded by NW–SE normal faults and filled by thick Pliocene–Quaternary deposits. A previous analysis of a giant piston core (LC09) from the Malta Graben had revealed a wide range of sedimentary features (carbonate turbidites, bioturbated mud and scours), although the chronostratigraphic constraint of the stacking pattern has remained elusive. After establishing a reliable chronological framework based on seven radiocarbon dates for a shorter core from the Malta Graben (ANSIC03-735), a down-core analysis of planktonic foraminifer and coccolith abundance, stable isotopes and sediment grain size was carried out. Since the last glacial maximum, palaeoenvironmental conditions (surface fertility and deep chlorophyll maximum during the last glacial and the Younger Dryas; warm and oligotrophic water masses, with a deep nutricline and intense winter mixing during the Holocene) as well as selected calcareous plankton taxa trends and peaks seem to be similar to those reported for other central and western Mediterranean sites, possibly in spite of a unique response of these areas to late Quaternary climatic fluctuations. Four distinct layers, each tens of centimetres thick, are barren of foraminifers but not of coccoliths. Morphobathymetric data as well as new high-resolution and high-penetration seismic profiles show that prolonged contouritic activity has persisted on the western side of the Malta Graben. It is thus likely that layers barren of foraminifers are due to the overflow of fine-grained (clayey) material beyond drift channel dikes.

Data Descriptor: A global multiproxy database for temperature reconstructions of the Common Era

PAGES, a core project of Future Earth, is supported by the U.S. and Swiss National Science Foundations. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Some of this work was conducted as part of the North America 2k Working Group supported by the John Wesley Powell Center for Analysis and Synthesis, funded by the U.S. Geological Survey. B. Bauer, W. Gross, and E. Gille (NOAA National Centers for Environmental Information) are gratefully acknowledged for helping assemble the data citations and creating the NCEI versions of the PAGES 2k data records. We thank all the investigators whose commitment to data sharing enables the open science ethos embodied by this project.

More roundabouts and reduced vehicle emissions

As a native Californian with approximately 10 years of European living and driving experience, I write on that personal favorite of British inventionsthe roundaboutand what it might do for reduced vehicle emissions (e.g., CO2 and other greenhouse gases). While the merits of installing roundabouts at intersections dominated by stop signs and traffic lights might be clear in terms of traffic flow efficiency, it is also worth highlighting from the more global perspective of potential emissions reductions. We are all aware of the benefits of reduced vehicle emissions, from the standpoint of either lowering the impacts or extending the lifespan of available fossil fuel resources, or both, but how many consider potential gains by simple traffic engineering adjustments with proven merit? Several European cities are increasing roundabout installations presumably with reduced congestion as the main motive, which is justified considering the growing and increasingly urbanized population. I would like to see this addressed in terms of global emissions as well, however. With no data, I aim to prompt a comparative and quantitative investigation on whether simple traffic-engineering adjustments might reduce emissions on the large-scale. I suspect the results may be encouraging and actually move policymakers (e.g., urban planners and traffic engineers) to act faster to install more roundabouts where they are needed most. While I have long pondered this, my recent California return and earning of a citation for not stopping at a stop-signed intersection has prompted renewed thought. Many intersections in California (and the U.S.) are dominated by stop signs, and under circumstances I suspect unwarranted by virtue of safety or traffic flow. I encourage the investigation of increased roundabouts, and whether fuel consumption and emissions decreases might both occur while also reducing congestion. Perhaps the results would quicken progressive change on a major modern issue.