Kristine L. DeLong

A reconstruction of sea surface temperature variability in the southeastern Gulf of Mexico from 1734 to 2008 C.E. using cross-dated Sr/Ca records from the coral Siderastrea siderea

This study uses skeletal variations in coral Sr/Ca from three Siderastrea siderea coral colonies within the Dry Tortugas National Park in the southeastern Gulf of Mexico (24°42′N, 82°48′W) to reconstruct monthly sea surface temperature (SST) variations from 1734 to 2008 Common Era (C.E.). Calibration and verification of the replicated coral Sr/Ca-SST reconstruction with local, regional, and historical temperature records reveals that this proxy-temperature relationship is stable back to 1879 C.E. The coral SST reconstruction contains robust interannual (~2.0°C) and multidecadal variability (~1.5°C) for the past 274 years, the latter of which does not covary with the Atlantic Multidecadal Oscillation. Winter SST extremes are more variable than summer SST extremes (±2.2°C versus ±1.6°C, 2σ) suggesting that Loop Current transport in the winter dominates variability on interannual and longer time scales. Summer SST maxima are increasing (+1.0°C for 274 years, σMC = ±0.5°C, 2σ), whereas winter SST minima contain no significant trend. Colder decades (~1.5°C) during the Little Ice Age (LIA) do not coincide with decades of sunspot minima. The coral SST reconstruction contains similar variability to temperature reconstructions from the northern Gulf of Mexico (planktic foraminifer Mg/Ca) and the Caribbean Sea (coral Sr/Ca) suggesting areal reductions in the Western Hemisphere Warm Pool during the LIA. Mean summer coral SST extremes post-1985 C.E. (29.9°C) exceeds the long-term summer average (29.2°C for 1734–2008 C.E.), yet the warming trend after 1985 C.E. (0.04°C for 24 years, σMC = ±0.5, 2σ) is not significant, whereas Caribbean coral Sr/Ca studies contain a warming trend for this interval.

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.

Obliquity pacing of the western Pacific Intertropical Convergence Zone over the past 282,000 years.

The Intertropical Convergence Zone (ITCZ) encompasses the heaviest rain belt on the Earth. Few direct long-term records, especially in the Pacific, limit our understanding of long-term natural variability for predicting future ITCZ migration. Here we present a tropical precipitation record from the Southern Hemisphere covering the past 282,000 years, inferred from a marine sedimentary sequence collected off the eastern coast of Papua New Guinea. Unlike the precession paradigm expressed in its East Asian counterpart, our record shows that the western Pacific ITCZ migration was influenced by combined precession and obliquity changes. The obliquity forcing could be primarily delivered by a cross-hemispherical thermal/pressure contrast, resulting from the asymmetric continental configuration between Asia and Australia in a coupled East Asian–Australian circulation system. Our finding suggests that the obliquity forcing may play a more important role in global hydroclimate cycles than previously thought.

North Pacific twentieth century decadal‐scale variability is unique for the past 342 years

Reconstructed sea surface temperatures (SSTs) derived from Mg/Ca measurements in nine encrusting coralline algal skeletons from the Aleutian archipelago in the northernmost Pacific Ocean reveal an overall increase in SST from 1665 to 2007. In the Aleutian SST reconstruction, decadal-scale variability is a transient feature present during the 1700s and early 1800s and then fully emerging post-1950. SSTs vary coherently with available instrument records of cyclone variance and vacillate in and out of coherence with multicentennial Pacific Northwest drought reconstructions as a response to SST-driven alterations of storm tracks reaching North America. These results indicate that an influence of decadal-scale variability on the North Pacific storm tracks only became apparent during the midtwentieth century. Furthermore, what has been assumed as natural variability in the North Pacific, based on twentieth century instrumental data, is not consistent with the long-term natural variability evident in reconstructed SSTs predating the anthropogenic influence.

A speleothem-based mid-Holocene precipitation reconstruction for West-Central Florida

The mid-Holocene was the warmest segment of the current interglacial and possessed a weak latitudinal temperature gradient, which impacted climate teleconnections and thus precipitation variability. Our window into the mid-Holocene climate is a high-resolution (near annual) stalagmite stable isotope-based paleoprecipitation record from Brown’s Cave in West-Central Florida. The oxygen isotopic (δ18O) time series is tied to a uranium-series (U-series) chronology that covers a 2000-year period from 6.6 to 4.6 ka. We compared our reconstruction with another speleothem δ18O-derived precipitation record near our study area that spans the last 1600 years. That comparison shows that the mid-Holocene was drier than the last 1.6 millennia. We posit the cause of this aridity was a westward expansion of the North Atlantic Subtropical High (NASH) coupled with changes in the planetary boundary layer in the Gulf of Mexico. Time-series analysis of our oxygen isotopic record found little evidence of any teleconnections originating from the North Atlantic including the North Atlantic Oscillation during the mid-Holocene. However, there is some indication of a weak, quasi-persistent oscillation within the temporal periodicity of the Atlantic Multidecadal Variability.

Recording Tropical Cyclone Activity from 1909 to 2014 along the Northern Gulf of Mexico using Maritime Slash Pine Trees (Pinus elliottii var. elliottii Engelm.)

ABSTRACT Tucker, C.S.; Trepanier, J.C.; Harley, G.L., and DeLong, K.L., 2018. Recording Tropical Cyclone Activity from 1909 to 2014 along the Northern Gulf of Mexico using Maritime Slash Pine Trees (Pinus elliottii var. elliottii Engelm.). The temporally incomplete tropical cyclone (TC) observational record limits the understanding of recurrence intervals and the impacts of repeated TCs on coastal ecosystems. Growth of maritime trees near the Gulf of Mexico may be affected by high winds, precipitation, and storm surges from TCs. Proxy records, such as tree growth recorded in annual ring widths, can be used to extend TC records temporally but must be verified with the observational record first. This study develops chronologies of total ring width (TRW), earlywood ring width (ERW), and latewood ring width (LRW) from slash pine (Pinus elliottii var. elliottii Engelm.) trees located 2 km from an open saltwater bay in the Grand Bay National Estuarine Research Reserve in coastal Mississippi, U.S.A. These chronologies are compared with TC storm surge and wind speed records using superposed epoch analysis. The year after a TC occurrence, tree growth is significantly (p < 0.05) suppressed (narrower than average annual growth rings) for TRW, ERW, and LRW with respect to storm surge and shows no statistical significance with high wind speeds. Individual trees display suppression in growth for 1–6 years after TC occurrences. This study demonstrates that slash pine trees in close proximity to salt water can be used to produce chronologies of TC occurrences for the northern Gulf of Mexico region and thus can eventually be used to extended and supplement temporally the existing TC observational record.

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.

Using Proxy Records to Document Gulf of Mexico Tropical Cyclones from 1820-1915

Observations of pre-1950 tropical cyclones are sparse due to observational limitations; therefore, the hurricane database HURDAT2 (1851–present) maintained by the National Oceanic and Atmospheric Administration may be incomplete. Here we provide additional documentation for HURDAT2 from historical United States Army fort records (1820–1915) and other archived documents for 28 landfalling tropical cyclones, 20 of which are included in HURDAT2, along the northern Gulf of Mexico coast. One event that occurred in May 1863 is not currently documented in the HURDAT2 database but has been noted in other studies. We identify seven tropical cyclones that occurred before 1851, three of which are potential tropical cyclones. We corroborate the pre-HURDAT2 storms with a tree-ring reconstruction of hurricane impacts from the Florida Keys (1707–2009). Using this information, we suggest landfall locations for the July 1822 hurricane just west of Mobile, Alabama and 1831 hurricane near Last Island, Louisiana on 18 August. Furthermore, we model the probable track of the August 1831 hurricane using the weighted average distance grid method that incorporates historical tropical cyclone tracks to supplement report locations.