Earth and Planetary Science Letters Evaluating controls on planktonic foraminiferal geochemistry in the Eastern Tropical North Pacific

To explore relationships between water column hydrography and foraminiferal geochemistry in the Eastern Tropical North Pacific, we present δ 18 O and Mg/Ca records from three species of planktonic foraminifera, Globigerinoides ruber , Globigerina bulloides , and Globorotalia menardii , collected from a sediment trap mooring maintained in the Gulf of Tehuantepec from 2006–2012. Differences in δ 18 O between mixed-layer species G. ruber and G. bulloides and thermocline-dweller G. menardii track seasonal changes in upwelling. The records suggest an increase in upwelling during the peak positive phase of El Niño, and an overall reduction in stratification over the six-year period. For all three species, Mg/Ca ratios are higher than what has been reported in previous studies, and show poor correlations to calcification temperature. We suggest that low pH (7.6–8.0) and [CO 32 − ] values ( ∼ 70–120 μmol/kg) in the mixed layer contribute to an overall trend of higher Mg/Ca ratios in this region. Laser Ablation Inductively Coupled Mass Spectrometry analyses of G. bulloides with high Mg/Ca ratios ( > 9 mmol/mol) reveal the presence of a secondary coating of inorganic calcite that has Mg/Ca and Mn/Ca ratios up to an order of magnitude higher than these elemental ratios in the primary calcite, along with elevated Sr/Ca and Ba/Ca ratios. Some of the samples with abnormally high Mg/Ca are found during periods of high primary productivity, suggesting the alteration may be related to changes in carbonate saturation resulting from remineralization of organic matter in oxygen-poor waters in the water column. Although similar shell layering has been observed on fossil foraminifera, this is the first time such alteration has been studied in shells collected from the water column. Our results suggest a role for seawater carbonate chemistry in influencing foraminiferal calcite trace element:calcium ratios prior to deposition on the seafloor, particularly in high-productivity, low-oxygen environments.

[1]  S. Alin,et al.  Influence of post‐Tehuano oceanographic processes in the dynamics of the CO2 system in the Gulf of Tehuantepec, Mexico , 2015 .

[2]  A. J. Smit,et al.  Under Pressure: Climate Change, Upwelling, and Eastern Boundary Upwelling Ecosystems , 2015, Front. Mar. Sci..

[3]  J. Erez,et al.  Revisiting carbonate chemistry controls on planktic foraminifera Mg / Ca: implications for sea surface temperature and hydrology shifts over the Paleocene–Eocene Thermal Maximum and Eocene–Oligocene Transition , 2015 .

[4]  S. Eggins,et al.  Optimizing LA-ICP-MS analytical procedures for elemental depth profiling of foraminifera shells , 2015 .

[5]  R. Poore,et al.  Globigerinoides ruber morphotypes in the Gulf of Mexico: A test of null hypothesis , 2014, Scientific Reports.

[6]  J. Hertzberg,et al.  Refining Globigerinoides ruber Mg/Ca paleothermometry in the Atlantic Ocean , 2013 .

[7]  P. deMenocal,et al.  The Influence of Salinity on Mg/Ca in Planktic Foraminifers – Evidence from Cultures, Core-top Sediments and Complementary δ18O , 2013 .

[8]  S. Eggins,et al.  Effect of dissolved oxygen concentration on planktonic foraminifera through laboratory culture experiments and implications for oceanic anoxic events , 2013 .

[9]  D. Schmidt,et al.  Mg/Ca in foraminifera from plankton tows: Evaluation of proxy controls and comparison with core tops , 2011 .

[10]  S. Eggins,et al.  Planktic foraminifers as recorders of seawater Ba/Ca , 2011 .

[11]  M. Kučera,et al.  Mg/Ca in the planktonic foraminifera Globorotalia inflata and Globigerinoides bulloides from Western , 2011 .

[12]  E. C. Farmer,et al.  On the fidelity of shell-derived δ18Oseawater estimates , 2010 .

[13]  R. Thunell,et al.  The oxygen isotope composition of planktonic foraminifera from the Guaymas Basin, Gulf of California: Seasonal, annual, and interspecies variability , 2010 .

[14]  J. McWilliams,et al.  High-frequency response of the ocean to mountain gap winds in the northeastern tropical Pacific , 2009 .

[15]  R. Tiedemann,et al.  Calibrating Mg/Ca ratios of multiple planktonic foraminiferal species with δ 18 O-calcification temperatures: Paleothermometry for the upper water column , 2009 .

[16]  J. Erez,et al.  Controls on shell Mg/Ca and Sr/Ca in cultured planktonic foraminiferan, Globigerinoides ruber (white) , 2008 .

[17]  J. Duplessy,et al.  Mg/Ca and Sr/Ca ratios in planktonic foraminifera: Proxies for upper water column temperature reconstruction , 2008, Paleoceanography.

[18]  M. Kučera,et al.  Systematic change of foraminiferal Mg/Ca ratios across a strong salinity gradient , 2008 .

[19]  G. Chavez,et al.  Recent planktonic foraminiferal distribution patterns and their relation to hydrographic conditions of the Gulf of Tehuantepec, Mexican Pacific , 2008 .

[20]  G. Reichart,et al.  Early diagenetic overprint in Caribbean sediment cores and its effect on the geochemical composition of planktonic foraminifera , 2007 .

[21]  Y. Hong,et al.  The TRMM Multisatellite Precipitation Analysis (TMPA): Quasi-Global, Multiyear, Combined-Sensor Precipitation Estimates at Fine Scales , 2007 .

[22]  Gavin A. Schmidt,et al.  Global gridded data set of the oxygen isotopic composition in seawater , 2006 .

[23]  F. Chavez,et al.  Primary production in the eastern tropical Pacific: A review , 2006 .

[24]  L. Löwemark,et al.  Mg/Ca ratios of two Globigerinoides ruber (white) morphotypes: Implications for reconstructing past tropical/subtropical surface water conditions , 2005 .

[25]  H. Elderfield,et al.  Variability of Mg/Ca and Sr/Ca between and within the planktonic foraminifers Globigerina bulloides and Globorotalia truncatulinoides , 2005 .

[26]  C. Pelejero,et al.  Identification and removal of Mn‐Mg‐rich contaminant phases on foraminiferal tests: Implications for Mg/Ca past temperature reconstructions , 2005 .

[27]  R. Thunell,et al.  Calibration of the planktonic foraminiferal Mg/Ca paleothermometer: Sediment trap results from the Guaymas Basin, Gulf of California , 2005 .

[28]  D. Lea,et al.  Seasonal and interannual variation in Santa Barbara Basin water temperatures observed in sediment trap foraminiferal Mg/Ca , 2004 .

[29]  B. Hönisch,et al.  Effects of seawater carbonate ion concentration and temperature on shell U, Mg, and Sr in cultured planktonic foraminifera , 2004 .

[30]  A. Mix,et al.  Oxygen isotopes, upper-ocean salinity, and precipitation sources in the eastern tropical Pacific , 2004 .

[31]  G. Wefer,et al.  Temperature:δ18O relationships of planktonic foraminifera collected from surface waters , 2003 .

[32]  H. Elderfield,et al.  A study of cleaning procedures used for foraminiferal Mg/Ca paleothermometry , 2003 .

[33]  J. O'Brien,et al.  Isthmus of Tehuantepec Wind Climatology and ENSO Signal , 2003 .

[34]  Henry Elderfield,et al.  Calibration of Mg/Ca thermometry in planktonic foraminifera from a sediment trap time series , 2003 .

[35]  D. Lea,et al.  Multispecies approach to reconstructing eastern equatorial Pacific thermocline hydrography during the past 360 kyr , 2003 .

[36]  D. Lea,et al.  Core top calibration of Mg/Ca in tropical foraminifera: Refining paleotemperature estimation , 2002 .

[37]  M. Kienast,et al.  A Comparison of Three Independent Paleotemperature Estimates From a High Resolution Record of Deglacial SST Records in the Tropical South China Sea , 2001 .

[38]  D. Lea,et al.  Climate impact of late quaternary equatorial pacific sea surface temperature variations , 2000, Science.

[39]  Luejiang Wang.  Isotopic signals in two morphotypes of Globigerinoides ruber (white) from the South China Sea: implications for monsoon climate change during the last glacial cycle , 2000 .

[40]  H. Elderfield,et al.  Past temperature and δ18O of surface ocean waters inferred from foraminiferal Mg/Ca ratios , 2000, Nature.

[41]  R. Healy,et al.  Global Distribution of Total Inorganic Carbon and Total Alkalinity below the Deepest Winter Mixed Layer Depths , 2000 .

[42]  H. Spero,et al.  Field examination of the oceanic carbonate ion effect on stable isotopes in planktonic foraminifera , 2000 .

[43]  F. Muller‐Karger,et al.  Characteristics of wind‐generated rings in the eastern tropical Pacific Ocean , 2000 .

[44]  D. Lea,et al.  Controls on magnesium and strontium uptake in planktonic foraminifera determined by live culturing , 1999 .

[45]  D. Lea,et al.  Glacial–interglacial changes in Subantarctic sea surface temperature and δ18O-water using foraminiferal Mg , 1999 .

[46]  Jelle Bijma,et al.  Reevaluation of the oxygen isotopic composition of planktonic foraminifera: Experimental results and revised paleotemperature equations , 1998 .

[47]  Jelle Bijma,et al.  Effect of seawater carbonate concentration on foraminiferal carbon and oxygen isotopes , 1997, Nature.

[48]  D. Canfield,et al.  Porewater pH and authigenic phases formed in the uppermost sediments of the Santa Barbara Basin , 1996 .

[49]  D. Antoine,et al.  Oceanic primary production: 2. Estimation at global scale from satellite (Coastal Zone Color Scanner) chlorophyll , 1996 .

[50]  M. Martínez-López,et al.  Oceanography of the Gulf of Tehuantepec, Mexico, indicated by Radiolaria remains , 1994 .

[51]  M. Machain-Castillo,et al.  Benthic foraminifera of the oxygen minimum zone, continental shelf of the Gulf of Tehuantepec, Mexico , 1990 .

[52]  F. Millero,et al.  A comparison of the equilibrium constants for the dissociation of carbonic acid in seawater media , 1987 .

[53]  J. Duplessy,et al.  Carbon and oxygen isotopic composition of planktonic foraminifera from laboratory culture, plankton tows and Recent sediment; implications for the reconstruction of paleoclimatic conditions and of the global carbon cycle , 1985 .

[54]  P. Wiebe,et al.  Vertical distribution and isotopic fractionation of living planktonic foraminifera from the Panama Basin , 1982, Nature.

[55]  H. Stumpf.  Satellite Detection of Upwelling in the Gulf of Tehuantepec, Mexico , 1975 .

[56]  C. Culberson,et al.  MEASUREMENT OF THE APPARENT DISSOCIATION CONSTANTS OF CARBONIC ACID IN SEAWATER AT ATMOSPHERIC PRESSURE1 , 1973 .

[57]  R. Clayton,et al.  Oxygen isotope fractionation in divalent metal carbonates , 1969 .

[58]  Timothy P. Boyer,et al.  World ocean atlas 2013. Volume 2, Salinity , 2002 .

[59]  H. Niebler,et al.  Oxygen Isotope Values of Planktic Foraminifera: A Tool for the Reconstruction of Surface Water Stratification , 1999 .

[60]  D. Günther,et al.  Inter-laboratory note. Laser ablation inductively coupled plasma mass spectrometric transient signal data acquisition and analyte concentration calculation , 1996 .

[61]  S. Gorshkov,et al.  World ocean atlas , 1976 .