Interglacial Pleistocene Periplatform Carbonate Δ13c as an Analogue for Interpreting Ancient Chemostratigraphies

Edmonsond, Stacey; Maloof, Adam C.; Nadeau, Matthew D.; Ahm, Anne‐Sofie C.; Geyman, Emily C.; Higgins, John A.; McGee, David; Stolper, Daniel A.

doi:10.1130/abs/2021am-368498

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“…Also, while the availability of condensation nuclei almost certainly plays a role in mud production, an estimated >98% of fine-grained suspended carbonate resides outside the visually dramatic whiting zone ( 47 ). Sedimentary records from the periplatform: For over 50 years, it has been known that there are thick accumulations of nonskeletal aragonite mud in the deep waters surrounding Bahama Banks ( 33 , 34 , 36 , 49 ) ( Fig. 5 ).…”

Section: Resultsmentioning

confidence: 99%

“…5 ). These muds have been assumed to represent export from the platform ( 33 , 36 , 49 ). The spatial and temporal records of these deep-water sedimentary deposits present two challenges to the whiting hypothesis.…”

Section: Resultsmentioning

confidence: 99%

“…5 ). Second, from the temporal perspective, sediment cores reveal thick accumulations of pristine aragonite mud ( 34 , 36 ) dated to the last glacial period ( 33 , 34 ) ( Fig. 5 C ).…”

Section: Resultsmentioning

confidence: 99%

“…Sedimentary records from the periplatform: For over 50 years, it has been known that there are thick accumulations of nonskeletal aragonite mud in the deep waters surrounding Bahama Banks ( 33 , 34 , 36 , 49 ) ( Fig. 5 ).…”

Section: Resultsmentioning

confidence: 99%

“…For example, 1) the old radiocarbon signature of suspended aragonite needles in whiting events ( 30 , 31 ) and 2) the lack of a drop in alkalinity in active whiting waters ( 8 , 21 , 30 ) both indicate that whitings are more likely to represent the resuspension of existing fine-grained sediment than the pseudohomogenous precipitation of new particles ( 8 , 31 ). Additionally, while the “whiting zone” has a relatively narrow geographic extent west of Andros Island ( 22 – 24 , 32 ), all of the basins surrounding the Bahama Banks are covered by thick blankets of carbonate mud ( 33 – 35 ), suggesting that mud is being exported from platforms that lack documented whiting events ( 33 ). In regard to the algal precipitation hypothesis ( 7 , 20 , 25 ), carbonate Sr concentration data have been used to argue that green algae cannot be the dominant source of Bahamian mud, since algal aragonite has lower Sr concentrations than bulk muds ( 36 ).…”

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confidence: 99%

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The origin of carbonate mud and implications for global climate

Geyman

Nadeau

et al. 2022

Proc. Natl. Acad. Sci. U.S.A.

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Carbonate mud represents one of the most important geochemical archives for reconstructing ancient climatic, environmental, and evolutionary change from the rock record. Mud also represents a major sink in the global carbon cycle. Yet, there remains no consensus about how and where carbonate mud is formed. Here, we present stable isotope and trace-element data from carbonate constituents in the Bahamas, including ooids, corals, foraminifera, and algae. We use geochemical fingerprinting to demonstrate that carbonate mud cannot be sourced from the abrasion and mixture of any combination of these macroscopic grains. Instead, an inverse Bayesian mixing model requires the presence of an additional aragonite source. We posit that this source represents a direct seawater precipitate. We use geological and geochemical data to show that “whitings” are unlikely to be the dominant source of this precipitate and, instead, present a model for mud precipitation on the bank margins that can explain the geographical distribution, clumped-isotope thermometry, and stable isotope signature of carbonate mud. Next, we address the enigma of why mud and ooids are so abundant in the Bahamas, yet so rare in the rest of the world: Mediterranean outflow feeds the Bahamas with the most alkaline waters in the modern ocean (>99.7th-percentile). Such high alkalinity appears to be a prerequisite for the nonskeletal carbonate factory because, when Mediterranean outflow was reduced in the Miocene, Bahamian carbonate export ceased for 3-million-years. Finally, we show how shutting off and turning on the shallow carbonate factory can send ripples through the global climate system.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

“…5 ). Second, from the temporal perspective, sediment cores reveal thick accumulations of pristine aragonite mud ( 34 , 36 ) dated to the last glacial period ( 33 , 34 ) ( Fig. 5 C ).…”

Section: Resultsmentioning

confidence: 99%