Investigation of a Northern brain , Diploria strigosa, for climate reconstructions PP33A-2099 Robin M. Cobb ([email protected]), Kristine L. DeLong, Jennifer A. Flannery, Alan D. Wanamaker, Jr., Christopher D. Reich, and J. Harold Hudson

Abstract 2. Coral Geochemistry and Growth Rates 3. SamplingArtifacts - Chipping during sampling

Paleoclimatologists have produced sea-surface temperature (SST) reconstructions from 0.9 4. Reduced coral geochemistry by sampling fast growing brain commonly found in the Atlantic 0.8 growth 5. Higher Sr/Ca Chipped area

Ocean. Many researchers avoid deeper coral reefs, >10-m water depth, because the 0.7 years Normal growth 0.6 geochemistry of these corals may not reflect SST due to water stratification and to avoid 0.5 Average = 0.51 cm 0.4 possible kinetic effects due to reduced coral growth with increasing water depth. Flower Warm 8.8 0.3 Garden Banks is the northernmost coral in the Gulf of Mexico with the top of the reef Extension Rate (cm) 8.9 at 18 m from the surface. In 1979, the U.S. Geological Survey recovered a core from a 3. Chips Sr/Ca mmol/mol) 9.0 Diploria strigosa colony in the East Flower Garden Bank (27°54'N, 93°35'W) from a Warm 9.1 9.0 –1 depth of ~21 m. Measurements of the x-radiographs reveal an average linear growth 9.1 20 samples year 9.2 Divots –1 9.1 rate of 0.51 cm year (±1.10, 1σ; n = 38). We analyzed approximately monthly samples 9.3 9.2 –1 18 20 samples year–1 9.2 (0.03 cm sample ) extracted along the growth axis for Sr/Ca and δ O. These Higher 9.4 Divots 9.3 Sr/Ca geochemical proxies for temperature reveal seasonal cycles; however, the section from 9.5 9.3 0 2 4 6 8 10 12 14 16 18 20 1968–1970 contains a 1.16% shift in the mean Sr/Ca with higher Sr/Ca values present 9.4

Depth (cm) Sr/Ca (mmol/mol) 9.4 only in the summer samples, resulting in a reduced seasonal cycle. Shifts in coral 9.5 geochemistry have been noted in other studies with the source of the shifts attributed to 10.0 10.5 11.0 11.5 12.0 12.5 Depth (cm) diagenesis, sampling artifacts, or growth effects. Our analysis of scanning electron microscope images did not find indications of diagenesis. To test if our sampling rate Annual cycles in Sr/Ca determinations is lost in chipped interval. biased our results, we sampled at a higher resolution (0.01 cm sample–1) and found similar results for Sr/Ca. The anomalous section coincides with a 39% reduction in linear 4. SamplingArtifacts - Sampling Resolution extension rates, leaving a growth effect as the remaining cause. This interval is not the

–1 coldest; the interval from 9–12 cm is colder with ≥ average extension rates. This interval 8.8 30 samples year Warm Divots coincides a negative Pacific/North American Pattern (PNA). We conclude that corals 8.9 from this deeper reef show promise for paleoclimate studies; however, further studies 9.0 are needed. 9.1 9.2 SST correlation map for EFB with 1. Location 9.3 OISST (Reynolds et al., 2002) Reduced –1 Sr/Ca (mmol/mol) 8 samples year 80º N growth 9.4 Divots

70º N 9.5

1940 9.6 60º N 0 0.5 1 1.5 2 2.5 3 3.5 4 1950 East Flower Garden Bank Depth (cm)

50º N 1960

1970 40º N Higher resolution sampling produced the same higher Sr/Ca 1979 30º N values (i.e., colder). We assume this is a growth related effect.

20º N SEM 5. Higher Sr/Ca but ≥ Extension Rates Depth (cm) 10º N 0 2 4 6 8 10 12 14 16 18 20 8.8

Warm 0º 100º W 80º W 60º W 40º W 20º W 0º 8.9 1978 1950

1940 8.9 Warm –0.4 –0.2 0 0.2 0.4 0.6 0.8 9.0 SEM samples - No diagenesis 9.0 1970 1960 AA B Diploria strigosa colonies July 2012 18 m depth Correlation Coefficient 9.1 Divots 9.1 9.2 30 samples year–1 9.3 9.2 8.9 Sr/Ca (mmol/mol) 9.4 9.3 9.0 Sr/Ca mmol/mol) Sr/Ca (mmol/mol) 9.5 9.1 9.4 20 samples year–1 Divots 9.2 0.6 Divots –1 9.5 8 samples year 9.3 0.4 PNA Index 9.4 0.2 C D –4.5 9.5 0. 0 Colder values not −0. 2 related to growth −0. 4 –3.5 −0. 6 effects. Possible −0. 8 –2.5 −1.0 connection to PNA. O (‰ VPDB) Divots 1980 1975 1970 1965 1960 1955 1950 18 –1 δ Time (years) –1.5 8 samples year 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 Depth (cm) Acknowledgements We would like to thank the St. Petersburg USGS and Dick Poore for coral samples. Tony Greco at the University of South for assistance with SEM imaging. Anna LaValley for drilling samples. Cyril Giry and Steffen Hetzinger for Reduced growth interval is not diagenesis, or sampling artifacts. helpful comments. NOAA Flower Garden Banks Down Under Out Yonder Workshop for allowing us to attend the workshop. Photo credit for images taken in the Flower Garden Banks goes to Aaron Gelfand.