The temporal and spatial patterns of late Holocene climate conditions provide valuable information for testing hypothesized mechanisms of recent climate changes. As a proxy for late Holocene climate in the southern tropics, we present a 10 Be chronology of moraines deposited by Qori Kalis, an outlet glacier of Quelccaya Ice Cap in Peru. The Qori Kalis moraines are located downfl ow from the Quelccaya ice cores and provide the fi rst glacial extent record that can be compared directly to annually resolved tropical ice core records. Qori Kalis advanced to its late Holocene maximum extent prior to 520 ± 60 yr before CE 2009, when Quelccaya ice core net accumulation values were at or below their late Holocene average. Subsequent glacial retreat between ~520 and 330 yr before CE 2009 coincides with the highest net accumulation values of the ~1800-yr-long ice core record. Therefore, we suggest that temperature, rather than net accumulation, was the primary driver of these glacial fl uctuations. Comparison of the late Holocene fl uctuations of Qori Kalis glacier with glaciers in the southern tropical Andes, Patagonian Andes, Switzerland, Alaska and New Zealand suggests globally synchronous, centennial-scale cold events.

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The climate of the southwestern North America has experienced profound changes between wet and dry phases over the past 200 Kyr. To better constrain the timing, magnitude, and paleoenvironmental impacts of these changes in hydroclimate, we conducted a multiproxy biomarker study from samples collected from a new 77 m sediment core (SLAPP‐SRLS17) drilled in Searles Lake, California. Here, we use biomarkers and pollen to reconstruct vegetation, lake conditions, and climate. We find that δD values of long chain n‐alkanes are dominated by glacial to interglacial changes that match nearby Devils Hole calcite δ18O variability, suggesting both archives predominantly reflect precipitation isotopes. However, precipitation isotopes do not simply covary with evidence for wet‐dry changes in vegetation and lake conditions, indicating a partial disconnect between large scale atmospheric circulation tracked by precipitation isotopes and landscape moisture availability. Increased crenarchaeol production and decreased evidence for methane cycling reveal a 10 Kyr interval of a fresh, productive, and well‐mixed lake during Termination II, corroborating evidence for a paleolake highstand from shorelines and spillover deposits in downstream Panamint Basin and Death Valley during the end of the penultimate (Tahoe) glacial (140–130 ka). At the same time brGDGTs yield the lowest temperature estimates (mean months above freezing = 9°C ± 3°C) of the 200 Kyr record. These limnological conditions are not replicated elsewhere in the 200 Kyr record, suggesting that the Heinrich stadial 11 highstand was wetter than the last glacial maximum and Heinrich 1 (18–15 ka).

Mercury (Hg) is a toxic metal that is transported globally through the atmosphere. Emissions

Both modern anthropogenic emissions of mercury (Hg), primarily from artisanal and small-scale gold mining (ASGM), and preindustrial anthropogenic emissions from mining are thought to have a large impact on present-day atmospheric Hg deposition. We study the spatial distribution of Hg and its depositional history over the past ~400 years in sediment cores from lakes located regionally proximal (~90–150 km) to the largest ASGM in Peru and distal (>400 km) to major preindustrial mining centers. Total Hg concentrations in surface sediments from fourteen lakes are typical of remote regions (10–115 ng g−1). Hg fluxes in cores from four lakes demonstrate preindustrial Hg deposition in southeastern Peru was spatially variable and at least an order of magnitude lower than previously reported fluxes in lakes located closer to mining centers. Average modern (A.D. 2000–2011) Hg fluxes in these cores are 3.4–6.9 μg m−2 a−1, compared to average preindustrial (A.D. 1800–1850) fluxes of 0.8–2.5 μg m−2 a−1. Modern Hg fluxes determined from the four lakes are on average 3.3 (±1.5) times greater than their preindustrial fluxes, similar to those determined in other remote lakes around the world. This agreement suggests that Hg emissions from ASGM are likely not significantly deposited in nearby downwind regions.

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a b s t r a c tImproving the late Quaternary paleoclimate record through climate interpretations of low-latitude glacier length changes advances our understanding of past climate change events and the mechanisms for past, present, and future climate change. Paleotemperature reconstructions at low-latitude glaciers are uniquely fruitful because they can provide both site-specific information and enhanced understanding of regional-scale variations due to the structure of the tropical atmosphere. We produce Little Ice Age (LIA) and Younger Dryas (YD) paleoclimate reconstructions for the Huancan e outlet glacier of the Quelccaya Ice Cap (QIC) and low-latitude southern hemisphere regional sea surface temperatures (SSTs) using a coupled ice-flow and energy balance model. We also model the effects of long-term changes in the summit temperature and precipitiation rate and the effects of interannual climate variability on the Huancan e glacier length. We find temperature to be the dominant climate driver of glacier length change. Also, we find that interannual climate variability cannot adequately explain glacier advances inferred from the geomorphic record, necessitating that these features were formed during past colder climates. To constrain our LIA reconstruction, we incorporate the QIC ice core record, finding a LIA air temperature cooling at the ice cap of between~0.7 C and~1.1 C and~0.4 C and regional SSTs cooling of~0.6 C. For the YD paleoclimate reconstructions, we propose two limits on the precipitation rate, since the ice core record does not extend into the Pleistocene: 1) the precipitation rate scales with the Clausius-Clapeyron relationship (upper limit on cooling) and 2) the precipitation rate increases by 40% (lower limit on cooling), which is an increase about twice as great as the regional increases realized in GCM simulations for the period. The first limit requires~1.6 C cooling in ice cap air temperatures and 0.9 C cooling in SSTs, and the second limit requires~1.0 C cooling in ice cap air temperatures and 0.5 C cooling in SSTs. Our temperature reconstructions are in good agreement with the magnitude and trend of GCM simulations that incorporate the forcing mechanisms hypothesized to have caused these climate change events.

Records of clastic sediment from lakes that receive glacial meltwater provide a means for inferring past glacial fluctuations. However, increased clastic sedimentation has been interpreted to indicate both glacial advance and recession. Here we examine the timing of clastic sediment deposition in Challpacocha, a glacially fed lake located downvalley from Quelccaya Ice Cap (QIC), Peru, in comparison with known ice cap margin fluctuations. Using a comparison with a nearby non-glacial lake, Yanacocha, we document that a record of clastic sediment flux from Challpacocha reflects meltwater-derived sediment. We then compare the clastic sediment record from Challpacocha with the Qori Kalis glacier moraine record. We find that organic-rich sediment was deposited primarily during the late Holocene advance of QIC (before $CE 1490). In contrast, clastic sediment was deposited during QIC recession ($CE 1490($CE -1970. Peaks in clastic sediment flux are associated with the onset of ice retreat. We suggest that this pattern of clastic sediment deposition reflects changing meltwater production and/ or glacial erosion during ice advance and retreat and supports models of increased clastic sedimentation during ice retreat.