Research

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Uplifted reef with corals of Holocene ages near Tanavusvus, Vanuatu in the southwest Pacific
Field photos courtesy of J. Partin & F. Taylor


Hover over images for captions

Drilling an  in situ  fossil coral head at Tasmaloum, Vanuatu (15.9°S, 166.9°E). The core extracted from this coral head is used to reconstruct climate variability during the Medieval Climate Anomaly (950-1250 CE).

Drilling an in situ fossil coral head at Tasmaloum, Vanuatu (15.9°S, 166.9°E). The core extracted from this coral head is used to reconstruct climate variability during the Medieval Climate Anomaly (950-1250 CE).

Top.  Southwest Pacfiic coral Sr/Ca-SST reconstructions for two Medieval Climate Anomaly fossil corals (11-TM-S5: green; 11-TM-I1: gray). The corals have ~23 years of overlap. Triangles indicate the 230Th ages ± 2σ analytical error.  Bottom.  Climatology-removed   Sr-Ca-SST anomalies for 11-TM-S5. The anomalies are 9-year high-pass filtered to isolate ENSO variability at internal (>1 - 9 yr) timescales.

Top. Southwest Pacfiic coral Sr/Ca-SST reconstructions for two Medieval Climate Anomaly fossil corals (11-TM-S5: green; 11-TM-I1: gray). The corals have ~23 years of overlap. Triangles indicate the 230Th ages ± 2σ analytical error. Bottom. Climatology-removed Sr-Ca-SST anomalies for 11-TM-S5. The anomalies are 9-year high-pass filtered to isolate ENSO variability at internal (>1 - 9 yr) timescales.

What is the range of natural (unforced) ENSO variability?

The El Niño-Southern Oscillation (ENSO) is the largest mode of interannual tropical climate variability. However, the instrumental record of ENSO is too short (<150 years) to quantify the full range of natural variability. Corals are a paleoclimate archive poised to address the limitations of instrumental data sets as they can provide decades to centuries of monthly-resolved climate data from the tropics.

This project uses replicated corals from the southwest Pacific to reconstruct ENSO-related sea surface temperature (SST) variability. We compare ENSO variability during the 20th century to variability ~900 years ago during the Medieval Climate Anomaly (MCA), a time interval when orbital, solar, and volcanic climate forcings were similar to pre-industrial values.

Few sub-annually resolved records of ENSO activity currently exist for the MCA. Our results address a spatial and temporal data gap and provide new insight to the range of observed ENSO activity.

Lawman, A.E., et al., A century of reduced ENSO variability during the Medieval Climate Anomaly, Nature Communications (in revision).

Watch me present at the 2017 AGU Fall Meeting (Session: Climate of the Common Era II)
Link to AGU On-Demand


How do uncertainties inherent to the coral archive impact our ability to reconstruct ENSO variability?

Coral records of surface ocean conditions extend our knowledge of ENSO variability to the pre-instrumental period. However, the ability to detect forced changes in ENSO using coral geochemical records is challenging due to multiple sources of uncertainties inherent to the coral archive. This project uses surface temperature and sea surface salinity output from the Community Earth System Model Last Millennium Ensemble to forward model pseudocoral geochemical time series. Different sources of uncertainty are incorporated into the coral proxy system model, allowing us to quantify how these factors impact the variance of a coral climate reconstruction. This work provides insight about coral site locations that are poised for detecting changes in ENSO variability.

Schematic for comparing climate model output with coral proxy-based climate reconstructions.  Clockwise left to right: climate model representation (credit: ©UCAR, image courtesy Gary Strand, NCAR). Coral polyp and underlying skeleton (painting: Geoff Kelly).  Porites lutea  coral (credit: National Park Service)

Schematic for comparing climate model output with coral proxy-based climate reconstructions. Clockwise left to right: climate model representation (credit: ©UCAR, image courtesy Gary Strand, NCAR). Coral polyp and underlying skeleton (painting: Geoff Kelly). Porites lutea coral (credit: National Park Service)


Uplifted reef at low tide (Tasmaloum, Vanuatu: 15.9°S, 166.9°E). Modern corals are located below present day sea level.  In situ  fossil coral heads spanning the last 2 millennium are in the foreground.

Uplifted reef at low tide (Tasmaloum, Vanuatu: 15.9°S, 166.9°E). Modern corals are located below present day sea level. In situ fossil coral heads spanning the last 2 millennium are in the foreground.

can we detect forced changes in enso over the holocene using CORAL reconstructions?

It is critical to ascribe the degree to which anthropogenic warming and internal climate variability are each contributing to future projections of ENSO in climate models. This motivates the use of paleo-ENSO reconstructions as out-of-sample tests of climate model simulations. This project focuses on generating new “snapshots” of ENSO variability from fossil corals of varying Holocene ages (past 10,000 years) from the Solomon Islands & Vanuatu in the southwest Pacific. The new data from the western Pacific will be combined with published Holocene coral data from the western and central equatorial Pacific to quantify ENSO variability over the Holocene.


Wet (blue) and dry (red) rainfall changes (units: mm/day) for the HadCM3 [Gordon et al., 2000; Pope et al. 2000] and IPSL [Marti et al., 2010] hosing experiments. Rainfall changes are relative to the Last Glacial Maximum background state (~21 ka). Maps modified from Kageyama et al. [2013],  Clim. Past.

Wet (blue) and dry (red) rainfall changes (units: mm/day) for the HadCM3 [Gordon et al., 2000; Pope et al. 2000] and IPSL [Marti et al., 2010] hosing experiments. Rainfall changes are relative to the Last Glacial Maximum background state (~21 ka). Maps modified from Kageyama et al. [2013], Clim. Past.

What is the response of tropical precipitation to abrupt climate change?

Paleoclimate data reveals coherent patterns of hydroclimate change during intervals when the high-latitude North Atlantic cools. Inspired by proxy evidence showing the reduced strength of the Atlantic Meridional Overturning Circulation (AMOC) during Heinrich Stadials “hosing” experiments in which freshwater is added to the high-latitude North Atlantic are widely performed to investigate the mechanisms that cause abrupt climate change

In this collaborative study involving both paleoclimate data and modelers, we investigate the global response of tropical precipitation during Heinrich Stadial 1 (~17-15 thousand years ago) by synthesizing published paleoclimate data. To explore the dynamical mechanisms responsible for communicating high-latitude signals to the global tropics, we incorporate climate model output from a suite of fifteen freshwater hosing experiments designed to simulate a reduction in AMOC.