Morphometric and stable isotopic differentiation of Orbulina universa morphotypes from the Cariaco Basin, Venezuela

Brittney J. Marshall; Robert C. Thunell; Howard J. Spero; Michael J. Henehan; Laura Lorenzoni; Yrene Astor

doi:10.1016/j.marmicro.2015.08.001

Morphometric and stable isotopic differentiation of Orbulina universa morphotypes from the Cariaco Basin, Venezuela

Brittney J. Marshall^*, Robert C. Thunell, Howard J. Spero, Michael J. Henehan, Laura Lorenzoni, Yrene Astor

^*Corresponding author for this work

School of Earth Sciences

Research output: Contribution to journal › Article (Academic Journal) › peer-review

35 Citations (Scopus)

Abstract

Biometric characteristics of Orbulina universa (d'Orbigny) were used to differentiate two morphotypes present in sediment trap samples collected from the Cariaco Basin, Venezuela. Specifically, wall thickness and weight-area relationships were used to separate shells into thin (M_thin) and thick (M_thick) morphotypes. M_thick (mean thickness=19-41μm) comprises 75% of the total O. universa in these samples and has morphometric characteristics similar to that of the previously described Type I Caribbean genotype, whereas M_thin (mean thickness=6-22μm) is comparable to the Type III Mediterranean genotype. The flux of M_thick increases during periods of upwelling, whereas M_thin flux shows no systematic relationship with changing hydrographic regimes in the basin. The δ¹⁸O and δ¹³C of M_thick are on average 0.34% higher and 0.38% lower, respectively, than those of M_thin, suggesting that they calcify their final spherical chamber at different depths in the water column and/or differ in their vital effects on shell geochemistry. Additionally, the absolute offset in the stable isotopic compositions of the two morphotypes varies as a function of surface ocean stratification. During periods of upwelling, the δ¹⁸O and δ¹³C absolute offsets between M_thin and M_thick are on average -0.15 and 0.25%, whereas average δ¹⁸O and δ¹³C absolute offsets between these two morphotypes increase to -0.54 and 0.41% during non-upwelling periods. We attribute the higher δ¹⁸O and δ¹³C offsets during non-upwelling periods to a difference in final chamber calcification depth and the combined effects of temperature (δ¹⁸O), δ¹³C_DIC (δ¹³C), irradiance (δ¹³C) and [CO₃^2-] (δ¹⁸O and δ¹³C). These data provide field evidence that thin and thick morphotypes of O. universa likely experience different environmental conditions during the formation of their final chamber and, therefore, should not be combined in geochemical analyses for reconstructing past surface ocean conditions. Finally, we introduce a new proxy for reconstructing past surface ocean stratification changes via the use of M_thin and M_thick δ¹⁸O and δ¹³C offsets.

Original language	English
Pages (from-to)	46-64
Number of pages	19
Journal	Marine Micropaleontology
Volume	120
DOIs	https://doi.org/10.1016/j.marmicro.2015.08.001
Publication status	Published - 1 Oct 2015

Bibliographical note

Funding Information:
We thank Eric Tappa for his analytical contributions, particularly with the collection of sediment trap samples and stable isotopic measurements. We thank the Fundación La Salle de Ciencias Naturales, Estación de Investigaciones Marinas Isla Margarita (EDIMAR) and the crew of the R/V Hermano Ginés for their hard work at maintaining the CARIACO Time Series. We thank Pincelli Hull of Yale University and Jay Pickney of University of South Carolina for their advice on concept and statistical assessment. This research was supported by NSF award 1258991 .

Publisher Copyright:
© 2015 Elsevier B.V.

Keywords

Cryptic species
Morphotypes
Orbulina universa
Planktonic foraminifera
Stable isotopes

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@article{16237e8671684e37be3d3cf7b99b0328,

title = "Morphometric and stable isotopic differentiation of Orbulina universa morphotypes from the Cariaco Basin, Venezuela",

abstract = "Biometric characteristics of Orbulina universa (d'Orbigny) were used to differentiate two morphotypes present in sediment trap samples collected from the Cariaco Basin, Venezuela. Specifically, wall thickness and weight-area relationships were used to separate shells into thin (Mthin) and thick (Mthick) morphotypes. Mthick (mean thickness=19-41μm) comprises 75% of the total O. universa in these samples and has morphometric characteristics similar to that of the previously described Type I Caribbean genotype, whereas Mthin (mean thickness=6-22μm) is comparable to the Type III Mediterranean genotype. The flux of Mthick increases during periods of upwelling, whereas Mthin flux shows no systematic relationship with changing hydrographic regimes in the basin. The δ18O and δ13C of Mthick are on average 0.34% higher and 0.38% lower, respectively, than those of Mthin, suggesting that they calcify their final spherical chamber at different depths in the water column and/or differ in their vital effects on shell geochemistry. Additionally, the absolute offset in the stable isotopic compositions of the two morphotypes varies as a function of surface ocean stratification. During periods of upwelling, the δ18O and δ13C absolute offsets between Mthin and Mthick are on average -0.15 and 0.25%, whereas average δ18O and δ13C absolute offsets between these two morphotypes increase to -0.54 and 0.41% during non-upwelling periods. We attribute the higher δ18O and δ13C offsets during non-upwelling periods to a difference in final chamber calcification depth and the combined effects of temperature (δ18O), δ13CDIC (δ13C), irradiance (δ13C) and [CO32-] (δ18O and δ13C). These data provide field evidence that thin and thick morphotypes of O. universa likely experience different environmental conditions during the formation of their final chamber and, therefore, should not be combined in geochemical analyses for reconstructing past surface ocean conditions. Finally, we introduce a new proxy for reconstructing past surface ocean stratification changes via the use of Mthin and Mthick δ18O and δ13C offsets.",

keywords = "Cryptic species, Morphotypes, Orbulina universa, Planktonic foraminifera, Stable isotopes",

author = "Marshall, {Brittney J.} and Thunell, {Robert C.} and Spero, {Howard J.} and Henehan, {Michael J.} and Laura Lorenzoni and Yrene Astor",

note = "Funding Information: We thank Eric Tappa for his analytical contributions, particularly with the collection of sediment trap samples and stable isotopic measurements. We thank the Fundaci{\'o}n La Salle de Ciencias Naturales, Estaci{\'o}n de Investigaciones Marinas Isla Margarita (EDIMAR) and the crew of the R/V Hermano Gin{\'e}s for their hard work at maintaining the CARIACO Time Series. We thank Pincelli Hull of Yale University and Jay Pickney of University of South Carolina for their advice on concept and statistical assessment. This research was supported by NSF award 1258991 . Publisher Copyright: {\textcopyright} 2015 Elsevier B.V.",

year = "2015",

month = oct,

day = "1",

doi = "10.1016/j.marmicro.2015.08.001",

language = "English",

volume = "120",

pages = "46--64",

journal = "Marine Micropaleontology",

issn = "0377-8398",

publisher = "Elsevier B.V.",

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TY - JOUR

T1 - Morphometric and stable isotopic differentiation of Orbulina universa morphotypes from the Cariaco Basin, Venezuela

AU - Marshall, Brittney J.

AU - Thunell, Robert C.

AU - Spero, Howard J.

AU - Henehan, Michael J.

AU - Lorenzoni, Laura

AU - Astor, Yrene

N1 - Funding Information: We thank Eric Tappa for his analytical contributions, particularly with the collection of sediment trap samples and stable isotopic measurements. We thank the Fundación La Salle de Ciencias Naturales, Estación de Investigaciones Marinas Isla Margarita (EDIMAR) and the crew of the R/V Hermano Ginés for their hard work at maintaining the CARIACO Time Series. We thank Pincelli Hull of Yale University and Jay Pickney of University of South Carolina for their advice on concept and statistical assessment. This research was supported by NSF award 1258991 . Publisher Copyright: © 2015 Elsevier B.V.

PY - 2015/10/1

Y1 - 2015/10/1

N2 - Biometric characteristics of Orbulina universa (d'Orbigny) were used to differentiate two morphotypes present in sediment trap samples collected from the Cariaco Basin, Venezuela. Specifically, wall thickness and weight-area relationships were used to separate shells into thin (Mthin) and thick (Mthick) morphotypes. Mthick (mean thickness=19-41μm) comprises 75% of the total O. universa in these samples and has morphometric characteristics similar to that of the previously described Type I Caribbean genotype, whereas Mthin (mean thickness=6-22μm) is comparable to the Type III Mediterranean genotype. The flux of Mthick increases during periods of upwelling, whereas Mthin flux shows no systematic relationship with changing hydrographic regimes in the basin. The δ18O and δ13C of Mthick are on average 0.34% higher and 0.38% lower, respectively, than those of Mthin, suggesting that they calcify their final spherical chamber at different depths in the water column and/or differ in their vital effects on shell geochemistry. Additionally, the absolute offset in the stable isotopic compositions of the two morphotypes varies as a function of surface ocean stratification. During periods of upwelling, the δ18O and δ13C absolute offsets between Mthin and Mthick are on average -0.15 and 0.25%, whereas average δ18O and δ13C absolute offsets between these two morphotypes increase to -0.54 and 0.41% during non-upwelling periods. We attribute the higher δ18O and δ13C offsets during non-upwelling periods to a difference in final chamber calcification depth and the combined effects of temperature (δ18O), δ13CDIC (δ13C), irradiance (δ13C) and [CO32-] (δ18O and δ13C). These data provide field evidence that thin and thick morphotypes of O. universa likely experience different environmental conditions during the formation of their final chamber and, therefore, should not be combined in geochemical analyses for reconstructing past surface ocean conditions. Finally, we introduce a new proxy for reconstructing past surface ocean stratification changes via the use of Mthin and Mthick δ18O and δ13C offsets.

AB - Biometric characteristics of Orbulina universa (d'Orbigny) were used to differentiate two morphotypes present in sediment trap samples collected from the Cariaco Basin, Venezuela. Specifically, wall thickness and weight-area relationships were used to separate shells into thin (Mthin) and thick (Mthick) morphotypes. Mthick (mean thickness=19-41μm) comprises 75% of the total O. universa in these samples and has morphometric characteristics similar to that of the previously described Type I Caribbean genotype, whereas Mthin (mean thickness=6-22μm) is comparable to the Type III Mediterranean genotype. The flux of Mthick increases during periods of upwelling, whereas Mthin flux shows no systematic relationship with changing hydrographic regimes in the basin. The δ18O and δ13C of Mthick are on average 0.34% higher and 0.38% lower, respectively, than those of Mthin, suggesting that they calcify their final spherical chamber at different depths in the water column and/or differ in their vital effects on shell geochemistry. Additionally, the absolute offset in the stable isotopic compositions of the two morphotypes varies as a function of surface ocean stratification. During periods of upwelling, the δ18O and δ13C absolute offsets between Mthin and Mthick are on average -0.15 and 0.25%, whereas average δ18O and δ13C absolute offsets between these two morphotypes increase to -0.54 and 0.41% during non-upwelling periods. We attribute the higher δ18O and δ13C offsets during non-upwelling periods to a difference in final chamber calcification depth and the combined effects of temperature (δ18O), δ13CDIC (δ13C), irradiance (δ13C) and [CO32-] (δ18O and δ13C). These data provide field evidence that thin and thick morphotypes of O. universa likely experience different environmental conditions during the formation of their final chamber and, therefore, should not be combined in geochemical analyses for reconstructing past surface ocean conditions. Finally, we introduce a new proxy for reconstructing past surface ocean stratification changes via the use of Mthin and Mthick δ18O and δ13C offsets.

KW - Cryptic species

KW - Morphotypes

KW - Orbulina universa

KW - Planktonic foraminifera

KW - Stable isotopes

UR - http://www.scopus.com/inward/record.url?scp=84944878923&partnerID=8YFLogxK

U2 - 10.1016/j.marmicro.2015.08.001

DO - 10.1016/j.marmicro.2015.08.001

M3 - Article (Academic Journal)

AN - SCOPUS:84944878923

SN - 0377-8398

VL - 120

SP - 46

EP - 64

JO - Marine Micropaleontology

JF - Marine Micropaleontology

ER -

Morphometric and stable isotopic differentiation of Orbulina universa morphotypes from the Cariaco Basin, Venezuela

Abstract

Bibliographical note

Keywords

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