Spatiotemporal variability of modern precipitation δ18O in the central Andes and implications for paleoclimate and paleoaltimetry estimates

Understanding the patterns of rainfall isotopic composition in the central Andes is hindered by sparse observations. Despite limited observational data, stable isotope tracers have been commonly used to constrain modern‐to‐ancient Andean atmospheric processes, as well as to reconstruct paleoclimate and paleoaltimetry histories. Here, we present isotopic compositions of precipitation (δ18Op and δDp) from 11 micrometeorological stations located throughout the Bolivian Altiplano and along its eastern flank at ~21.5°S. We collected and isotopically analyzed 293 monthly bulk precipitation samples (August 2008 to April 2013). δ18Op values ranged from −28.0‰ to 9.6‰, with prominent seasonal cycles expressed at all stations. We observed a strong relationship between the δ18Op and elevation, though it varies widely in time and space. Constraints on air sourcing estimated from atmospheric back trajectory calculations indicate that continental‐scale climate dynamics control the interannual variability in δ18Op, with upwind precipitation anomalies having the largest effect. The impact of precipitation anomalies in distant air source regions to the central Andes is in turn modulated by the Bolivian High. The importance of the Bolivian High is most clearly observed on the southern Bolivian Altiplano. However, monthly variability among Altiplano stations can exceed 10‰ in δ18Op on the plateau and cannot be explained by elevation or source variability, indicating a nontrivial role for local scale effects on short timescales. The strong influence of atmospheric circulation on central Andean δ18Op requires that paleoclimate and paleoaltimetry studies consider the role of South American atmospheric paleocirculation in their interpretation of stable isotopic values as proxies.Key PointsFive‐year record of central Andes precipitation isotopic compositionPrecipitation isotopes are elevation dependent, but vary in space and timePrecipitation isotope variability is related to large‐scale climate dynamicsPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/111974/1/jgrd52161.pd

Dynamic and Thermodynamic Influences on Precipitation in Northeast Mexico on Orbital to Millennial Timescales

The timing and mechanisms of past hydroclimate change in northeast Mexico are poorly constrained, limiting our ability to evaluate climate model performance. To address this, we present a multiproxy speleothem record of past hydroclimate variability spanning 62.5 to 5.1 ka from Tamaulipas, Mexico. Here we show a strong influence of Atlantic and Pacific sea surface temperatures on orbital and millennial scale precipitation changes in the region. Multiple proxies show no clear response to insolation forcing, but strong evidence for dry conditions during Heinrich Stadials. While these trends are consistent with other records from across Mesoamerica and the Caribbean, the relative importance of thermodynamic and dynamic controls in driving this response is debated. An isotope-enabled climate model shows that cool Atlantic SSTs and stronger easterlies drive a strong inter-basin sea surface temperature gradient and a southward shift in moisture convergence, causing drying in this region

Finishing the euchromatic sequence of the human genome

The sequence of the human genome encodes the genetic instructions for human physiology, as well as rich information about human evolution. In 2001, the International Human Genome Sequencing Consortium reported a draft sequence of the euchromatic portion of the human genome. Since then, the international collaboration has worked to convert this draft into a genome sequence with high accuracy and nearly complete coverage. Here, we report the result of this finishing process. The current genome sequence (Build 35) contains 2.85 billion nucleotides interrupted by only 341 gaps. It covers ∼99% of the euchromatic genome and is accurate to an error rate of ∼1 event per 100,000 bases. Many of the remaining euchromatic gaps are associated with segmental duplications and will require focused work with new methods. The near-complete sequence, the first for a vertebrate, greatly improves the precision of biological analyses of the human genome including studies of gene number, birth and death. Notably, the human enome seems to encode only 20,000-25,000 protein-coding genes. The genome sequence reported here should serve as a firm foundation for biomedical research in the decades ahead

How obliquity cycles powered early Pleistocene global ice‐volume variability

Milankovitch theory proposes that the magnitude of high‐latitude summer insolation dictates the continental ice‐volume response by controlling summer snow melt, thus anticipating a substantial ice‐volume contribution from the strong summer insolation signal of precession. Yet almost all of the early Pleistocene δ18O records' signal strength resides at the frequency of obliquity. Here we explore this discrepancy using a climate‐vegetation‐ice sheet model to simulate climate‐ice sheet response to transient orbits of varying obliquity and precession. Spectral analysis of our results shows that despite contributing significantly less to the summer insolation signal, almost 60% of the ice‐volume power exists at the frequency of obliquity due to a combination of albedo feedbacks, seasonal offsets, and orbital cycle duration differences. Including eccentricity modulation of the precession ice‐volume component and assuming a small Antarctic ice response to orbital forcing produce a signal that agrees with the δ18O ice‐volume proxy records.Key PointsClimate responses to orbital changes simulated with an Earth system modelModel produces a larger ice‐volume response to obliquity than precessionModel results agree with early Pleistocene oxygen isotope recordsPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/111096/1/grl52691-sup-0001-SIGRL.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/111096/2/grl52691.pd

One-Continent and Two-Continents atmosphere outputs, links to netCDF files

Atmospheric data associated with "Climate responses to the splitting of a supercontinent: Implications for the breakup of Pangea" by Tabor et al. (2019; GRL). Files contain climatologies of FLNS, FLNSC, FLNT, FLNTC, FSNS, FSNSC, FSNT, FSNTC, LHFLX, LWCF, OMEGA, PRECC, PRECL, PS, SHFLX, SWCF, TS, U, and V variables for the One Continent and Two Continents geographic configurations discussed in the manuscript

Green Sahara Simulations with iCESM

Files contain monthly climatologies of surface temperature, 2m temperature, sea level pressure, precipitation, and d18O of precipitation from 50-year averages of the preindustrial control, mid-Holocene with desert Sahara, and mid-Holocene with vegetated Sahara experiments discussed in the manuscript

How obliquity cycles powered early Pleistocene global ice‐volume variability

Milankovitch theory proposes that the magnitude of high‐latitude summer insolation dictates the continental ice‐volume response by controlling summer snow melt, thus anticipating a substantial ice‐volume contribution from the strong summer insolation signal of precession. Yet almost all of the early Pleistocene δ18O records' signal strength resides at the frequency of obliquity. Here we explore this discrepancy using a climate‐vegetation‐ice sheet model to simulate climate‐ice sheet response to transient orbits of varying obliquity and precession. Spectral analysis of our results shows that despite contributing significantly less to the summer insolation signal, almost 60% of the ice‐volume power exists at the frequency of obliquity due to a combination of albedo feedbacks, seasonal offsets, and orbital cycle duration differences. Including eccentricity modulation of the precession ice‐volume component and assuming a small Antarctic ice response to orbital forcing produce a signal that agrees with the δ18O ice‐volume proxy records.Key PointsClimate responses to orbital changes simulated with an Earth system modelModel produces a larger ice‐volume response to obliquity than precessionModel results agree with early Pleistocene oxygen isotope recordsPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/111096/1/grl52691-sup-0001-SIGRL.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/111096/2/grl52691.pd

Simulations of the Impact Winter at the Cretaceous-Paleogene Boundary

Monthly atmospheric data associated with "Causes and Climatic Consequences of the Impact Winter at the Cretaceous-Paleogene Boundary" by Tabor et al. (GRL). Files contain TS, TREFHT, FSDS, FSDSC, FSNS, FLDS, FLNS, SHFLX, LHFLX, PRECC, PRECL, and QFLX variables for the 30-year averaged Maastrichtian control, and 20-year transient soot emission, SO2 emission, and dust emission experiments discussed in the manuscript