Neritic ecosystem response to Oceanic Anoxic Event 2 in the Cretaceous Western Interior Seaway, USA

Carbon Cycling During Oceanic Anoxic Event 2: Compound‐Specific Carbon Isotope Evidence From the Western Interior Seaway

“…All biomarkers show the pronounced positive CIE at the onset of OAE2 (Table 1; Figures 2 and 3), though the magnitude of that CIE differs between biomarkers (Table 1; Supporting Information ). Pristane and phytane show a CIE magnitude that is, consistent with that of bulk OM and carbonate, while other biomarkers such as steranes and hopanes show a much larger CIE magnitude (Table 1), likely due to changes in source organisms (i.e., input of soil bacteria below 122 mcd; Boudinot et al., 2020) and biosynthetic pathways (e.g., steranes; Supporting Information ).…”

“…Bentonite layers, biostratigraphic indicators, astrochronology, and carbon isotope chemostratigraphy have aided in the basin‐wide and global correlation of the SH#1 core with other OAE2 sections (Jones et al., 2019). Existing records from the SH#1 core, including carbon isotopes from bulk carbonate (δ 13 C carb ) and organic matter (OM; δ 13 C org ), and the diversity and abundance of lipid biomarkers and foraminifera, provide extensive information on the ecological dynamics at the core location during OAE2 (Boudinot et al., 2020; Jones et al., 2019).…”

“…Biomarkers were extracted and purified as described in Boudinot et al. (2020). In brief, cleaned and powdered rock samples were extracted using a Dionex Accelerated Solvent Extractor (ASE) 200 with a mixture of dichloromethylene and methanol (DCM:MeOH 9:1 v:v).…”

“…Oceanic Anoxic Event 2 (OAE2; ∼94 Ma) was an interval of global change characterized by elevated atmospheric CO 2 (Freeman & Hayes, 1992; Bice et al., 2006; Hong & Lee, 2012; Sinninghe Damsté et al., 2008; Witkowski et al., 2018), altered nutrient cycling (Monteiro et al., 2012; Mort et al., 2007; Owens et al., 2016), and expanded ocean anoxia (Boudinot et al., 2020; Kuypers et al., 2002; Monteiro et al., 2012; Owens et al., 2013, 2016; Pancost et al., 2004; Sarmiento et al., 1988; Schlanger & Jenkyns, 1976; Sepúlveda et al., 2009; Takashima et al., 2006) making it a useful case study to investigate the effects of global climate change on marine biogeochemistry. Previous studies have revealed that the rapid input of mantle‐derived CO 2 and nutrients before OAE2 (Barclay et al., 2010; DuVivier et al., 2014; Jones et al., 2020; Turgeon & Creasser, 2008) resulted in enhanced marine productivity (Kuypers et al., 2002; Leckie et al., 2002; Monteiro et al., 2012; Mort et al., 2007; Sepúlveda et al., 2009), water column deoxygenation (Boudinot et al., 2020; Kuypers et al., 2002; Monteiro et al., 2012; Owens et al., 2013, 2016; Pancost et al., 2004; Sepúlveda et al., 2009; Takashima et al., 2006), increased ocean temperature (Bice et al., 2006; Huber et al., 2002; O'Brien et al., 2017; Wilson & Norris, 2001), and ultimately widespread marine organic carbon burial during OAE2 (Arthur et al., 1987; Schlanger & Jenkyns, 1976). Questions remain, however, concerning the nature of the carbon cycle perturbations within the OAE2 event itself (e.g., Boudinot & Sepúlveda, 2020; O'Connor et al., 2019).…”

“…Detailed questions concerning the timing and nature of biogeochemical feedbacks around OAE2, including the direct response of marine ecosystems to changes in p CO 2 , the oceanographic controls on marine productivity, and the timing of CO 2 inputs at the onset of the event, require higher temporal resolution p CO 2 and productivity records. The Smokey Hollow #1 core (SH#1 core; Figure 1) presents an expanded sedimentary record of OAE2 from the western margin of the Western Interior Seaway (WIS; Jones et al., 2019) that contains both marine‐derived and terrestrially derived biomarkers (Boudinot & Sepúlveda, 2020; Boudinot et al., 2020), providing a high‐resolution archive of marine and atmospheric carbon, respectively. Using carbon isotopes of biomarkers in the SH#1 core, we test the hypotheses that (a) carbon isotopes from marine‐derived and terrestrial‐derived biomarkers preserved in neritic ecosystems record changes in global and local carbon cycle dynamics, (b) that OAE2 was spurred by a pulse of CO 2 to the atmosphere before the event, (c) that the onset (initial CIE) of OAE2 was characterized by a unilateral drawdown of atmospheric and aqueous CO 2 , and (d) that the Plenus event experienced multiple pulses of enhanced atmospheric CO 2 input.…”