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Abstract Lacustrine carbonates are a powerful archive of paleoenvironmental information but are susceptible to post‐depositional alteration. Microbial metabolisms can drive such alteration by changing carbonate saturationin situ, thereby driving dissolution or precipitation. The net impact these microbial processes have on the primary δ¹⁸O, δ¹³C, and Δ₄₇values of lacustrine carbonate is not fully known. We studied the evolution of microbial community structure and the porewater and sediment geochemistry in the upper ~30 cm of sediment from two shoreline sites at Green Lake, Fayetteville, NY over 2 years of seasonal sampling. We linked seasonal and depth‐based changes of porewater carbonate chemistry to microbial community composition, in situ carbon cycling (using δ¹³C values of carbonate, dissolved inorganic carbon (DIC), and organic matter), and dominant allochems and facies. We interpret that microbial processes are a dominant control on carbon cycling within the sediment, affecting porewater DIC, aqueous carbon chemistry, and carbonate carbon and clumped isotope geochemistry. Across all seasons and sites, microbial organic matter remineralization lowers the δ¹³C of the porewater DIC. Elevated carbonate saturation states in the sediment porewaters (Ω > 3) were attributed to microbes from groups capable of sulfate reduction, which were abundant in the sediment below 5 cm depth. The nearshore carbonate sediments at Green Lake are mainly composed of microbialite intraclasts/oncoids, charophytes, larger calcite crystals, and authigenic micrite—each with a different origin. Authigenic micrite is interpreted to have precipitated in situ from the supersaturated porewaters from microbial metabolism. The stable carbon isotope values (δ¹³C_carb) and clumped isotope values (Δ₄₇) of bulk carbonate sediments from the same depth horizons and site varied depending on both the sampling season and the specific location within a site, indicating localized (μm to mm) controls on carbon and clumped isotope values. Our results suggest that biological processes are a dominant control on carbon chemistry within the sedimentary subsurface of the shorelines of Green Lake, from actively forming microbialites to pore space organic matter remineralization and micrite authigenesis. A combination of biological activity, hydrologic balance, and allochem composition of the sediments set the stable carbon, oxygen, and clumped isotope signals preserved by the Green Lake carbonate sediments. 

Abstract BackgroundDespite many initiatives to improve graduate student and faculty diversity in engineering, there has been little or no change in the percentage of people from racially minoritized backgrounds in either of these groups. Purpose/HypothesisThe purpose of this paper is to counter the scarcity fallacy, in which institutions blame the “shortage” of qualified people from traditionally marginalized backgrounds for their own lack of representation, related to prospective PhD students and prospective faculty from traditionally marginalized groups. This study identifies the BS‐to‐PhD and PhD‐to‐tenure‐track‐faculty institutional pathways of Black/African American and Hispanic/Latino engineering doctorate recipients. Design/MethodUsing the US Survey of Earned Doctorates, we tracked the BS‐to‐PhD institutional pathways of 3952 Black/African American and 5732 Hispanic/Latino engineering PhD graduates. We also used the Survey of Doctorate Recipients to track the PhD‐to‐tenure‐track faculty pathways of 104 Black/African American and 211 Hispanic/Latino faculty. ResultsThe majority of Black/African American and Hispanic/Latino PhD graduates in this study did not earn their BS degrees from Top 25 institutions, but rather from Not Top 25, non‐US, and minority‐serving institutions. The results also show the relatively small proportion of PhD earners and faculty members who move into highly ranked institutions after earning a bachelor's degree from outside this set of institutions. ConclusionsThe findings of this study have important implications for graduate student and faculty recruitment by illustrating that recruitment from a narrow range of institutions (i.e., Top 25 institutions) is unlikely to result in increased diversity among racially minoritized PhDs and faculty in engineering. 

Abstract Organic and inorganic stable isotopes of lacustrine carbonate sediments are commonly used in reconstructions of ancient terrestrial ecosystems and environments. Microbial activity and local hydrological inputs can alter porewater chemistry (e.g., pH, alkalinity) and isotopic composition (e.g., δ¹⁸O_water, δ¹³C_DIC), which in turn has the potential to impact the stable isotopic compositions recorded and preserved in lithified carbonate. The fingerprint these syngenetic processes have on lacustrine carbonate facies is yet unknown, however, and thus, reconstructions based on stable isotopes may misinterpret diagenetic records as broader climate signals. Here, we characterize geochemical and stable isotopic variability of carbonate minerals, organic matter, and water within one modern lake that has known microbial influences (e.g., microbial mats and microbialite carbonate) and combine these data with the context provided by 16S rRNA amplicon sequencing community profiles. Specifically, we measure oxygen, carbon, and clumped isotopic compositions of carbonate sediments (δ¹⁸O_carb, δ¹³C_carb, ∆₄₇), as well as carbon isotopic compositions of bulk organic matter (δ¹³C_org) and dissolved inorganic carbon (DIC; δ¹³C_DIC) of lake and porewater in Great Salt Lake, Utah from five sites and three seasons. We find that facies equivalent to ooid grainstones provide time‐averaged records of lake chemistry that reflect minimal alteration by microbial activity, whereas microbialite, intraclasts, and carbonate mud show greater alteration by local microbial influence and hydrology. Further, we find at least one occurrence of ∆₄₇isotopic disequilibrium likely driven by local microbial metabolism during authigenic carbonate precipitation. The remainder of the carbonate materials (primarily ooids, grain coatings, mud, and intraclasts) yield clumped isotope temperatures (T(∆₄₇)), δ¹⁸O_carb, and calculated δ¹⁸O_waterin isotopic equilibrium with ambient water and temperature at the time and site of carbonate precipitation. Our findings suggest that it is possible and necessary to leverage diverse carbonate facies across one sedimentary horizon to reconstruct regional hydroclimate and evaporation–precipitation balance, as well as identify microbially mediated carbonate formation. 

Abstract Pollen, the microgametophyte of seed plants, has an important role in plant reproduction and, therefore, evolution. Pollen is variable in, for example, size, shape, aperture number; these features are particularly diverse in some plant taxa and can be diagnostic. In one family, Boraginaceae, the range of pollen diversity suggests the potential utility of this family as a model for integrative studies of pollen development, evolution and molecular biology. In the present study, a comprehensive survey of the diversity and evolution of pollen from 538 species belonging to 72 genera was made using data from the literature and additional scanning electron microscopy examination. Shifts in diversification rates and the evolution of various quantitative characters were detected, and the results revealed remarkable differences in size, shape and number of apertures. The pollen of one subfamily, Boraginoideae, is larger than that in Cynoglossoideae. The diversity of pollen shapes and aperture numbers in one tribe, Lithospermeae, is greater than that in the other tribes. Ancestral pollen for the family was resolved as small, prolate grains that bear three apertures and are iso‐aperturate. Of all the tribes, the greatest number of changes in pollen size and aperture number were observed in Lithospermeae and Boragineae, and the number of apertures was found to be stable throughout all tribes of Cynoglossoideae. In addition, the present study showed that diversification of Boraginaceae cannot be assigned to a single factor, such as pollen size, and the increased rate of diversification for species‐rich groups (e.g.Cynoglossum) is not correlated with pollen size or shape evolution. The palynological data and patterns of character evolution presented in the study provide better resolution of the roles of geographical and ecological factors in the diversity and evolution of pollen grains of Boraginaceae, and provide suggestions for future palynological research across the family.