Limits on the ventilation rate for the deep ocean over the last 12000 years

In this paper we present accelerator radiocarbon measurements on hand picked benthic and planktonic foraminifera separated from two deep sea cores raised from the South China Sea. From the benthic-planktonic age differences we are able to place limits on the extent to which the ventilation rate of the deep Pacific Ocean has changed over the last 12000 years. While much work remains to be done before any definitive answers for the global oceans can be given, these results on cores with sedimentation rates suitably high to avoid major corrections for bioturbation effects suggest that the ventilation rate of the deep Pacific Ocean has remained nearly the same throughout Holocene time. Further, there is no suggestion that the rate was slower during the period of major glacial retreat. These results confirm that the changes in atmospheric¹⁴C/C ratio over the last 10000 years owe their origin to radiocarbon production rate changes.     

Evidence from Ar/Ar Ages of Individual Hornblende Grains for Varying Laurentide Sources of Iceberg Discharges 22,000 to 10,500 yr B.P.

The abundance and lithic content of ice rafted detritus in glacial North Atlantic sediment cores vary abruptly on millennial time scales that have been correlated to Dansgaard-Oeschger cycles in the Greenland ice cores. There is growing evidence that various ice sheet outlets contributed increased iceberg fluxes at multiple discrete intervals, and the relative timing of iceberg discharges from different sources is important for understanding interactions between oceans and ice sheets. We present a provenance study based on ⁴⁰Ar/³⁹Ar dates of individual hornblende grains from 20 samples taken at 600 to 700 yr spacing between 10,500 and 22,000 yr B.P., from Orphan Knoll core EW9303-GGC31. Heinrich layers are characterized by a dominant Paleoproterozoic hornblende provenance consistent with published studies. A change in provenance between Heinrich events H2 and H1 indicates contributions of iceberg calving from the Newfoundland and southern Labrador margins. Between H1 and the Younger Dryas interval, Paleoproterozoic ice rafted grains remained dominant. The dominance of Baffin Island (or Greenland?) sources to the ice rafted detritus is ascribed to the retreat of the southern Laurentide ice sheet at about the time of H1—a retreat that isolated Newfoundland and southern Labrador ice from the shelf-slope boundary.     

Slave ownership and fossil fuel usage: a commentary

In a recent, thought-provoking article, Jean-François Mouhot argues that there are many similarities between historical slave ownership and present-day fossil fuel usage. For that reason, Mouhot believes, members of modern fossil-fuel-dependent civilization should not feel morally superior to slave owners. While it is easy to sympathize with Mouhot’s intentions of furthering a transition to sustainable energy use, some arguments made in the article are in need of refinement.     

Differences in groundwater response to deforestation — a continuum of interactions between hydroclimate,landscape characteristics and time

After several decades of catchment research, most forest hydrologists agree that deforestation leads to increased annual catchment yields and augment groundwater recharge and dry-season flow. Nevertheless, millions of people in the semi-arid tropics have good reasons — a deep knowledge of the land after using it for many generations — to state the very opposite, ie that deforestation implies dry springs and streams. In this paper a model is presented which attemps to show that both of the above views are correct, but only if the hydrological consequences of deforestation are related to the diversity in land management, hydroclimate and landscape characteristics. The possibility of closing the dichotomy of opinion between people and professionals is discussed.     

Origin of the northern Atlantic's Heinrich events

As first noted by Heinrich, 1988, glacial age sediments in the eastern part of the northern Atlantic contain layers with unusually high ratios of ice-rafted lithic fragments to foraminifera shells. He estimated that these layers are spaced at intervals of roughly 10 000 years. In this paper we present detailed information documenting the existence of the upper five of these layers in ODP core 609 from 50° N and 24° W. Their ages are respectively 15 000 radiocarbon years, 20 000 radiocarbon years, 27 000 radiocarbon years, about 40 000 years, and about 50 000 years. We also note that the high lithic fragment to foram ratio is the result of a near absence of shells in these layers. Although we are not of one mind regarding the origin of these layers, we lean toward an explanation that the Heinrich layers are debris released during the melting of massive influxes of icebergs into the northern Atlantic. These sudden inputs may be the result of surges along the eastern margin of the Laurentide ice sheet.Contribution to Clima Locarno — Past and Present Climate Dynamics; Conference September 1990, Swiss Academy of Sciences — National Climate Program     

Effects of thermal energy storage on shallow aerobic aquifer systems: temporary increase in abundance and activity of sulfate-reducing and sulfur-oxidizing bacteria

Aquifer thermal energy storage may result in increases in the groundwater temperature up to 70 °C and more. This may lead to geochemical and microbiological alterations in the aquifer. To study the temperature effects on the indigenous microbial community composition, sediment column experiments at four different temperatures were carried out and the effluents were characterized geochemically and microbiologically. After an equilibrium phase at groundwater temperature of 10 °C for 136 days, one column was kept at 10 °C as a reference and the others were heated to 25, 40 and 70 °C. Genetic fingerprinting and quantitative PCR revealed a change in the bacterial community composition and abundance due to the temperature increase. While at 25 °C only slight changes in geochemical composition and gene copy numbers for bacteria were observed, increasing concentrations of total organic carbon in the 40 °C column were followed by a strong increase in bacterial abundance. Thermophilic bacteria became dominant at 70 °C. Temporary sulfate reduction took place at 40 and 70 °C and this correlated with an increased abundance of sulfate-reducing bacteria (SRB). Furthermore, a coexistence of SRB and sulfur-oxidizing bacteria (SOB) at all temperatures indicated an interaction of these physiological groups in the sediments. The results show that increased temperatures led to significant shifts in the microbial community composition due to the altered availability of electron donors and acceptors. The interplay of SRB and SOB in sedimentary biofilms facilitated closed sulfur cycling and diminished harmful sulfur species.