Shannon E. Loomis

Continental arc volcanism as the principal driver of icehouse-greenhouse variability.

Erosion overwhelmed by eruption Volcanism and erosion can feed into long-term climate change, but determining their relative importance is challenging. Erosion is known to be a carbon sink and is thought to play an outsized role in shifting global climate. However, McKenzie et al. suggest that long-term oscillations in climate may be tied to the amount of continental arc volcanism (see the Perspective by Kump). A global compilation of arc volcano-produced zircons over the past 700 million years revealed good correlation between warm and cool epochs with the waxing and waning of volcanism. Thus, volcanism may be a more important driver and erosion a less important sink for very long-term climate changes. Science, this issue p. 444; see also p. 411 A global analysis of detrital zircons suggests that volcanism is the primary driver of very long-term climate oscillations. [Also see Perspective by Kump] Variations in continental volcanic arc emissions have the potential to control atmospheric carbon dioxide (CO2) levels and climate change on multimillion-year time scales. Here we present a compilation of ~120,000 detrital zircon uranium-lead (U-Pb) ages from global sedimentary deposits as a proxy to track the spatial distribution of continental magmatic arc systems from the Cryogenian period to the present. These data demonstrate a direct relationship between global arc activity and major climate shifts: Widespread continental arcs correspond with prominent early Paleozoic and Mesozoic greenhouse climates, whereas reduced continental arc activity corresponds with icehouse climates of the Cryogenian, Late Ordovician, late Paleozoic, and Cenozoic. This persistent coupled behavior provides evidence that continental volcanic outgassing drove long-term shifts in atmospheric CO2 levels over the past ~720 million years.

The tropical lapse rate steepened during the Last Glacial Maximum

A new temperature record from East Africa demonstrates that the tropical lapse rate steepened during the last ice age. The gradient of air temperature with elevation (the temperature lapse rate) in the tropics is predicted to become less steep during the coming century as surface temperature rises, enhancing the threat of warming in high-mountain environments. However, the sensitivity of the lapse rate to climate change is uncertain because of poor constraints on high-elevation temperature during past climate states. We present a 25,000-year temperature reconstruction from Mount Kenya, East Africa, which demonstrates that cooling during the Last Glacial Maximum was amplified with elevation and hence that the lapse rate was significantly steeper than today. Comparison of our data with paleoclimate simulations indicates that state-of-the-art models underestimate this lapse-rate change. Consequently, future high-elevation tropical warming may be even greater than predicted.

Expanded glaciers during a dry and cold Last Glacial Maximum in equatorial East Africa

Glaciers on the worlds highest tropical mountains are among the most sensitive components of the cryosphere, yet the climatic controls that infl uence their fl uctuations are not fully under- stood. Here we present the fi rst 10 Be ages of glacial moraines in Africa and use these to assess the climatic conditions that infl uenced past tropical glacial extents. We applied 10 Be surface exposure dating to determine the ages of quartz-rich boulders atop moraines in the Rwenzori Mountains (~1°N, 30°E), located on the border of Uganda and the Democratic Republic of Congo. The 10 Be ages document expanded glaciers ca. 23.4 and 20.1 ka, indicating that glaciers in equatorial East Africa advanced during the global Last Glacial Maximum (ca. 26-19.5 ka). A comparison of these moraine ages with regional paleoclimate records indicates that Rwen- zori glaciers expanded contemporaneously with dry and cold conditions. Recession from the moraines occurred after ca. 20.1 ka, similar in timing to a rise in air temperature documented in East African lake records. Our results suggest that, on millennial time scales, past fl uctua- tions of Rwenzori glaciers were strongly infl uenced by air temperature.

Corrigendum to “Distributions of 5- and 6-methyl branched glycerol dialkyl glycerol tetraethers (brGDGTs) in East African lake sediment: Effects of temperature, pH, and new lacustrine paleotemperature calibrations” [Org. Geochem. 117 (2018) 56–69]

The authors regret that in this paper there were three mistakes in formulae in the statistical methods section. The authors would like to apologize for any inconvenience caused. Eq. (1) should read: [Formula presented] Eq. (2) should read: [Formula presented] Eq. (3) should read: [Formula presented]