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#gdgts

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Nina Davtian

On this #InternationalWomensDay, let me highlight two #WomenInSTEM.
First, Amy Cromartie, who leads the following @EuroGeosciences #preprint:
egusphere.copernicus.org/prepr
Second, Devika Varma, who recently defended her #PhD #thesis. Her PhD work at @NIOZnieuws aimed to investigate #paleotemperature indicators based on #archaeal hydroxylated #tetraether #lipids (OH-isoGDGTs):
nioz.nl/en/news/investigating-
#IWD #IWD25 #IWD2025
#Science #ScienceMastodon #AcademicMastodon
#GDGTs #brGDGTs #isoGDGTs
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egusphere.copernicus.orgUtilizing Probability Estimates from Machine Learning and Pollen to Understand the Depositional Influences on Branched GDGT in Wetlands, Peatlands, and LakesAbstract. Branched glycerol dialkyl glycerol tetraethers (brGDGTs) serve as critical molecular biomarkers for the quantitative reconstruction of past environments, ambient temperature and pH across various archives. Despite their success, numerous issues persist that limit their application. The distribution of brGDGTs varies significantly based on provenance, resulting in biases in environmental reconstructions that rely on fractional abundances and derived indices, such as the MBT’5ME. This issue is especially significant in shallow lakes, wetlands, and peatlands within semi-arid and arid regions, where ecosystems are sensitive to diverse environmental and climatic factors. Recent advancements, such as machine learning techniques, have been developed to identify changes in sources; however, these techniques are insufficient for detecting mixed source environments. The probability estimates derived from five machine learning algorithms are employed here to detect provenance changes in brGDGT downcore records and to identify periods of mixed provenance. A new global modern database (n=2301) was compiled to train, validate, test, and apply these algorithms to two sedimentary records. Our findings are corroborated by pollen and non-pollen palynomorphs obtained from the identical records. These microfossil proxies are utilized to discuss changes in provenance, hydrology, and ecology that influence the distribution of brGDGTs. Probability estimates derived from Random Forest with a sigmoid calibration are most effective in detecting changes in brGDGT distribution. Minor changes in the relative contributions of brGDGTs provenance can significantly influence the distribution of brGDGTs, especially regarding the MBT'5ME index. This study introduces a novel brGDGT wetland index aimed at monitoring potential biases arising from wetland development.
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Nina Davtian

On this #InternationalDayOfWomenAndGirlsInScience, here is a great story presented in two papers led by a #WomanInScience (Jingjing Guo) and last authored by another #WomanInScience (Francien Peterse).

#Scientific #publication #1: doi.org/10.5194/cp-21-343-2025
Scientific publication #2: doi.org/10.1016/j.orggeochem.2

#Science
#ScienceMastodon
#AcademicMastodon
#PaleoClimate
#PaleoHydrology
#EastAsianMonsoon
#PaleoTemperature
#OrganicGeochemistry
#GDGTs #brGDGTs
#ClimateProxies #Loess
#IDWGS #IDWGS2025

doi.orgTowards quantitative reconstruction of past monsoon precipitation based on tetraether membrane lipids in Chinese loessAbstract. Variations in the oxygen isotope composition (δ18O) of cave speleothems and numerous proxy records from loess–paleosol sequences have revealed past variations in East Asian monsoon (EAM) intensity. However, challenges persist in reconstructing precipitation changes quantitatively. Here, we use the positive relationship between the degree of cyclization (DC) of branched glycerol dialkyl glycerol tetraethers (brGDGTs) in modern surface soils from the Chinese Loess Plateau (CLP) and mean annual precipitation (MAP) to quantify past monsoon precipitation changes on the CLP. We present a new ∼ 130 000-year-long DC-based MAP record for the Yuanbao section on the western edge of the CLP, which closely tracks the orbital- and millennial-scale variations in available records of both speleothem δ18O and the hydrogen isotope composition of plant waxes (δ2Hwax) from the same section. Combing our new data with existing brGDGT records from other CLP sites reveals a spatial gradient in MAP that is most pronounced during glacials, when the western CLP experiences more arid conditions and receives up to ∼ 250 mm less precipitation than in the southeast, whereas MAP is ∼ 850 mm across the CLP during the Holocene optimum. Furthermore, the DC records show that precipitation amount on the CLP varies at both the precession scale and the obliquity scale, as opposed to the primarily precession-scale variations in speleothem δ18O and δ2Hwax at Yuanbao and the 100 kyr cycle in other loess proxies, such as magnetic susceptibility, which rather indicates the relative intensity of the EAM. At the precession scale, the DC record is in phase with δ2Hwax from the same section and the speleothem δ18O record, which supports the hypothesis that monsoon precipitation is driven by Northern Hemisphere summer insolation.
Public
Nina Davtian

Are past #ocean #temperature #reconstructions based on #geochemical indicators representative at the #local and #regional scales, as such reconstructions typically rely on a single #sediment core?
This new #scientific #publication—not co-authored by me—addresses this #question:
doi.org/10.1186/s40645-024-006
#Science
#ScienceMastodon #AcademicMastodon
#PaleoClimate #SeaTemperature #SeaSurfaceTemperature #SST
#Geochemistry #Foraminifera #MgCa #Biomarkers #Alkenones #GDGTs #isoGDGTs

SpringerOpenReplicability of paleotemperature records in the northern Okinawa Trough and its implications for paleoceanographic reconstructions - Progress in Earth and Planetary ScienceGeochemical proxies are frequently utilized in the reconstruction of past ocean temperatures. Due to resource constraints, these reconstructions typically rely on a single sediment core, raising questions about the local and regional representativeness of paleotemperature records. To address this, we analyzed four sediment cores located within a 10-km radius in the northern Okinawa Trough (OT), which share the same climatic forcing and thus should reflect similar climate variations. We compiled published data and generated new paleotemperature estimates based on three widely used geochemical proxies (foraminiferal Mg/Ca, $${\text{U}}_{37}^{{{\text{K}}^{\prime}}}$$ U 37 K ′ , $${\text{TEX}}_{86}$$ TEX 86 ). Analysis of the mean absolute deviations for nearby records based on the same proxy revealed that $${\text{U}}_{37}^{{{\text{K}}^{\prime}}}$$ U 37 K ′ has the highest reproducibility, followed by Mg/Ca and $${\text{TEX}}_{86}$$ TEX 86 . However, inconsistencies in inter-proxy offsets among nearby sites suggest the presence of noise in the proxy records, likely stemming from instrumental errors and sediment heterogeneity. Furthermore, the Mg/Ca and $${\text{U}}_{37}^{{{\text{K}}^{\prime}}}$$ U 37 K ′ paleotemperature records agree within uncertainty when accounting for inter-site variability and calibration uncertainties, challenging previous interpretations of temperature signals from different seasons. All proxies indicate similar glacial-interglacial trends, albeit with varying magnitudes of temperature change. Both Mg/Ca and $${\text{U}}_{37}^{{{\text{K}}^{\prime}}}$$ U 37 K ′ records suggest a glacial cooling of ~ 3 °C, whereas $${\text{TEX}}_{86}$$ TEX 86 sea surface temperature (SST) data indicate a stronger glacial cooling of approximately ~ 6–8 °C. Modern observations indicate a subsurface $${\text{TEX}}_{86}$$ TEX 86 recording depth of 50–100 m, coinciding with the thermocline. However, the $${\text{TEX}}_{86}$$ TEX 86 subsurface temperature (subT) record does not resemble the Mg/Ca records of thermocline-dwelling foraminifera species. Instead, there is a better agreement with benthic foraminiferal Mg/Ca records of Uvigerina spp. (~ 700 m) and the intermediate temperature record derived from radiolarian assemblages (~ 500 m), pointing to a $${\text{TEX}}_{86}$$ TEX 86 recording depth that is deeper than the thermocline. In summary, our findings show that proxy noise can impact inter-proxy comparisons of paleotemperature records, but not the direction of glacial-interglacial shifts. Future research should prioritize constraining the recording depth of paleotemperature proxies and reducing calibration uncertainty for more precise and reliable quantitative paleotemperature reconstruction.
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Nina Davtian

Over the past few years, I substantially contributed to the OH-isoGDGT #literature (Davtian et al., 2019 PALO; 2021 PALO; Davtian & Bard, 2023 PNAS), so I am overjoyed to highlight this new OH-isoGDGT #scientific #publication by Devika Varma et al. in #Biogeosciences @EuroGeosciences!
doi.org/10.5194/bg-21-4875-202
Disclaimer: I am not a co-author and I did not review this #paper either.
#Science
#ScienceMastodon #AcademicMastodon
#Archaea #Microbiology #Cultures
#Biomarkers #GDGTs #isoGDGTs

doi.orgControls on the composition of hydroxylated isoprenoidal glycerol dialkyl glycerol tetraethers (isoGDGTs) in cultivated ammonia-oxidizing ThaumarchaeotaAbstract. Membrane lipids of ammonia-oxidizing Thaumarchaeota, in particular isoprenoidal glycerol dialkyl glycerol tetraethers (isoGDGTs) and hydroxylated isoGDGTs (OH-isoGDGTs), have been used as biomarkers and as proxies in various environments. Controlled growth experiments have been used to investigate the factors that influence the composition of these lipids, in particular on how these factors affect the TEX86 temperature proxy, which is based on the degree of cyclization of isoGDGTs. Recently, the ring index of OH-isoGDGTs (RI-OH′), based on cyclization patterns of OH-isoGDGTs, and the abundance of OH-isoGDGTs relative to summed abundances of OH-isoGDGTs and regular isoGDGTs (% OH) have emerged as promising temperature proxies. Here, we examined the impact of growth temperature and growth phase on the distribution of OH-isoGDGTs and their associated proxies using cultures of two thaumarchaeotal strains. Analysis of core lipids and headgroup compositions of isoGDGTs and OH-isoGDGTs showed no consistent differences between the mid-exponential and stationary phases for both strains. Nitrosopumilus adriaticus NF5 shows a substantially higher relative abundance of OH-isoGDGTs (∼ 49 %) compared to Nitrosopumilus piranensis D3C (∼ 5 %) and also relative to observations reported for core lipids in the marine environment (< 17 %), indicating large variations in % OH values even among closely related species. Unlike in the marine environment, the % OH did not decrease with increasing temperatures in either of the strains, possibly reflecting a threshold below 15 °C for this response in the natural environment. The RI-OH′ increases with increasing temperature in cultures of both strains, similar to the ring index of regular isoGDGTs. The relative abundances of the headgroups varied between strains and did not respond to changes in temperature or growth phase. The % OH and RI-OH′ calculated from intact polar lipids with different headgroups revealed large differences between the distinct intact polar lipids, similar to that previously observed for regular isoGDGTs. Together, our findings suggest that growth temperature has a pronounced effect on the degree of cyclization in isoGDGTs and OH-isoGDGTs, in contrast to the relative abundance of OH-isoGDGTs, which mainly exhibits interspecies variability.
Public
Nina Davtian

Let me explain in the following #thread why the (auto-)citation of Davtian et al. (2018) Organic Geochemistry—my second first-authored #PhD #scientific #publication—by De Jonge et al. (2024) Geochemistry, Geophysics, Geosystems matters to me and my current CEREGE colleagues at CEREGE
doi.org/10.1016/j.orggeochem.2 👇🏻 (1/9)
#Science
#ScienceMastodon #AcademicMastodon
#Paper
#GDGTs #isoGDGTs #brGDGTs
#Index #Indices #ClimateProxies
#LiquidChromatography #MassSpectrometry
mastodon.world/@nina_davtian/1

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Nina Davtian

I am honored to co-author the new #scientific #publication first-authored by Petter Hällberg! This time, it is the use of #levoglucosan rather than #GDGTs—as #paleohydrology rather than #paleotemperature #ClimateProxies this time!—which granted me this #collaboration and co-authorship!
doi.org/10.1016/j.quascirev.20
More information in the following thread: 👇🏻 (1/6)
#Science
#ScienceMastodon #AcademicMastodon
#Paper #OpenAccess #OpenAccessWeek #OpenAccessWeek24 #OpenAccessWeek2024
#isoGDGTs #brGDGTs

Header of the online article by Hällberg et al. (2024) QSR (https://doi.org/10.1016/j.quascirev.2024.108948) entitled "Disentangling seasonal and annual precipitation signals in the tropics over the Holocene: Insights from δD, alkanes and GDGTs" and published as a gold open access paper in the Elsevier journal Quaternary Science Reviews. Screenshot taken by Nina Davtian (that's me!).
ALT
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Nina Davtian

I am so glad to be one of the two ICTA-UAB representants—the other is Joan Villanueva—for the interlaboratory #study led by Cindy De Jonge and Francien Peterse!
doi.org/10.1029/2024GC011583
Let's summarize this important #scientific #publication with the following #thread! 👇🏻 (1/6)
#Science
#ScienceMastodon #AcademicMastodon
#WomenInSTEM
#Paper #OpenAccess #OpenAccessWeek #OpenAccessWeek24 #OpenAccessWeek2024
#RoundRobin #Reproducibility
#LiquidChromatography #MassSpectrometry
#GDGTs #brGDGTs

Header of the online article by De Jonge et al. (2024) GGG (https://doi.org/10.1029/2024GC011583) entitled "Interlaboratory Comparison of Branched GDGT Temperature and pH Proxies Using Soils and Lipid Extracts" and published as a gold open access paper in the AGU journal Geochemistry, Geophysics, Geosystems. The author list is organized as follows: the first two authors (Cindy De Jonge and Francien Peterse) led the study and contributed equally to the paper, with the help of the third and fourth authors (Klaas G. J. Nierop and Thomas M. Blattmann), whereas the rest of the authors (including me, Nina Davtian) are (mostly) ordered alphabetically as representants of the participating laboratories. Screenshot taken by Nina Davtian (that's me!).
ALT
Public
Nina Davtian

Isn't it cool to see papers that cite one of yours and one of the papers that you reviewed*** and liked? #GDGTs
*Kou et al. (2024 QSR, 2024 PAL³)
doi.org/10.1016/j.quascirev.20
doi.org/10.1016/j.palaeo.2024.
**Wu et al. (2024 GRL)
doi.org/10.1029/2023GL107280
***I seldom sign my review reports for submitted papers, but I made a few exceptions and in the case of the OH-isoGDGT paper by Wu et al., the authors publicly thanked me and two anonymous co-reviewers, so readers may know this anyways.

#Science
#PeerReview

Public *
Nina Davtian

Two #basic #things to #know for #GDGT #lovers like me:
- These #nerdy #membrane-spanning #lipids are #ubiquitous in the #environment
- #GDGTs may have #multiple and #mixed #sources

If like a younger me* you apply #TEX86 in (#paleo)prodelta #deposits, be prepared to obtain #spooky #results from this #GDGT-based #paleotemperature #ClimateProxy!
#Links to the related #research #publication and #source #data in my auto-reply 👇🏻

*Me when I was a #PhDStudent

#HappyHalloween2024

@gdgt

Figure 3 in Davtian et al. (2019) Paleoceanography and Paleoclimatology (https://doi.org/10.1029/2018PA003452) All plotted sedimentary records from the Gulf of Lion, western Mediterranean Sea, cover the 160 to 9 ka BP period. (a) A sea surface temperature record from an established organic paleotemperature proxy named TEX86, which shows some spooky features. (b) A very qualitative and imperfect record of terrigenous inputs, which shows many similarities with TEX86 in terms of trends. (c) A sea surface temperature record from a recent organic paleotemperature proxy named RI-OH, which typically shows the expected behavior over the covered time period. (d) Another good-looking sea surface temperature record but from the most established organic paleotemperature proxy named UK'37. (e) A good-looking record from an established inorganic (non-strictly) paleotemperature proxy named d18O, with a reversed y-axis because foraminiferal d18O values decrease when sea temperatures increase.
ALT
Figure 4 in Davtian et al. (2019) Paleoceanography and Paleoclimatology (https://doi.org/10.1029/2018PA003452) Essentially the same caption as for Figure 3 in Davtian et al. (2019) Paleoceanography and Paleoclimatology, but with a focus on the 70 to 20 ka BP period.
ALT
Public
Nina Davtian

Are #nerdy #membrane-spanning #lipids produced by #bacteria and #archaea admitted on #Mastodon?

These lipids, named glycerol dialkyl glycerol tetraethers (#GDGTs), are my favorite #biomarkers for their usefulness as #climatic and #environmental #indicators and for having been the #protagonists of my #PhD #research.

Recently, I participated to an #international #workshop organized by #GDGT #nerds for GDGT nerds, sadly not active on this #platform as far as I know.

Nerdy mug with two of Nina Davtian's favorite membrane-spanning lipids on it. The molecule drawn in green is a bacterial membrane lipid whereas the molecule drawn in blue, red, and yellow is a famous archaeal membrane lipid named crenarchaeol.
ALT
Same nerdy mug as in the other photo but viewed from the other side. The name of the (niche) international workshop to which Nina Davtian participated in September 2023 and the name of the city where this workshop was organized are visible. GDGT stands for "glycerol dialkyl glycerol tetraether" and is the abbreviated name of Nina Davtian's favorite membrane-spanning lipids.
ALT
#Science#ScienceMastodon
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