Late Pliocene sea-ice expansion and its influence on diatom species turnover in the Southern Ocean

Ishino, Saki; Suto, Itsuki

doi:10.1016/j.marmicro.2020.101895

Cited by 6 publications

(3 citation statements)

References 45 publications

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“…Lags of a similar magnitude were not unusual during Pleistocene glacial inceptions (Petit et al, 1999). Marginal Antarctic diatom assemblages and lithology suggest that considerable sea ice expansion occurred during M2, which could have inhibited CO 2 outgassing from the deep ocean (Ishino and Suto, 2020;McKay et al, 2012). Moreover, a slight increase in dust-mediated iron fertilization of the Southern Ocean may have facilitated export productivity (Martínez-Garcia et al, 2011).…”

Section: Latementioning

confidence: 88%

A 15-million-year surface- and subsurface-integrated TEX₈₆ temperature record from the eastern equatorial Atlantic

et al. 2022

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Abstract. TEX86 is a paleothermometer based on Thaumarcheotal glycerol dialkyl glycerol tetraether (GDGT) lipids and is one of the most frequently used proxies for sea-surface temperature (SST) in warmer-than-present climates. However, GDGTs are not exclusively produced in and exported from the mixed layer, so sedimentary GDGTs may contain a depth-integrated signal that is also sensitive to local subsurface temperature variability. In addition, the correlation between TEX86 and SST is not significantly stronger than that to depth-integrated mixed-layer to subsurface temperatures. The calibration of TEX86 to SST is therefore controversial. Here we assess the influence of subsurface temperature variability on TEX86 using a downcore approach. We present a 15 Myr TEX86 record from Ocean Drilling Program Site 959 in the Gulf of Guinea and use additional proxies to elucidate the source of the recorded TEX86 variability. Relatively high GDGT[2/3] ratio values from 13.6 Ma indicate that sedimentary GDGTs were partly sourced from deeper (>200 m) waters. Moreover, late Pliocene TEX86 variability is highly sensitive to glacial–interglacial cyclicity, as is also recorded by benthic δ18O, while the variability within dinoflagellate assemblages and surface/thermocline temperature records (U37k′ and Mg/Ca) is not primarily explained by glacial–interglacial cyclicity. Combined, these observations are best explained by TEX86 sensitivity to sub-thermocline temperature variability. We conclude that TEX86 represents a depth-integrated signal that incorporates a SST and a deeper component, which is compatible with the present-day depth distribution of Thaumarchaeota and with the GDGT[2/3] distribution in core tops. The depth-integrated TEX86 record can potentially be used to infer SST variability, because subsurface temperature variability is generally tightly linked to SST variability. Using a subsurface calibration with peak calibration weight between 100 and 350 m, we estimate that east equatorial Atlantic SST cooled by ∼5 ∘C between the Late Miocene and Pleistocene. On shorter timescales, we use the TEX86 record as a proxy for South Atlantic Central Water (SACW), which originates from surface waters in the South Atlantic Gyre and mixes at depth with Antarctic Intermediate Water (AAIW). Leads and lags around the Pliocene M2 glacial (∼3.3 Ma) in our record, combined with published information, suggest that the M2 glacial was marked by SACW cooling during an austral summer insolation minimum and that decreasing CO2 levels were a feedback, not the initiator, of glacial expansion.

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Section: Latementioning

confidence: 88%

A 15-million-year surface- and subsurface-integrated TEX₈₆ temperature record from the eastern equatorial Atlantic

et al. 2022

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“…Lags of a similar magnitude were not unusual during Pleistocene glacial inceptions (Petit et al, 1999). Marginal Antarctic diatom assemblages and lithology suggest that considerable sea ice expansion occurred during M2, which could have inhibited CO2 outgassing from the deep ocean (Ishino and Suto, 2020;McKay et al, 2012). Moreover, a slight increase in dust-mediated iron fertilization of the Southern Ocean may have facilitated export productivity (Martínez-Garcia et al, 2011).…”

Section: Late Neogene Tex86 As An Intermediate Ocean Signal At Site 959: New Insights In M2 Glacial Inceptionmentioning

confidence: 89%

A fifteen-million-year surface- and subsurface-integrated TEX<sub>86</sub> temperature record from the eastern equatorial Atlantic

Weijst

Laan

Peterse

et al. 2021

Preprint

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Abstract. TEX86 is a paleothermometer based on Thaumarcheotal glycerol dialkyl glycerol tetraether (GDGT) lipids and is one of the most frequently used proxies for sea-surface temperature (SST) in warmer-than-present climates. However, the calibration of TEX86 to SST is controversial because its correlation to SST is not significantly stronger than that to depth-integrated surface to subsurface temperatures. Because GDGTs are not exclusively produced in and exported from the surface ocean, sedimentary GDGTs may contain a depth-integrated signal that is sensitive to local subsurface temperature variability, which can only be proved in downcore studies. Here, we present a 15 Myr TEX86 record from ODP Site 959 in the Gulf of Guinea and use additional proxies to elucidate the source of the recorded TEX86 variability. Relatively high GDGT[2/3] ratio values from 13.6 Ma indicate that sedimentary GDGTs were partly sourced from deeper (> 200 m) waters. Moreover, late Pliocene TEX86 variability is highly sensitive to glacial-interglacial cyclicity, as is also recorded by benthic δ18O, while the variability within dinoflagellate assemblages and surface/thermocline temperature records (Uk’37 and Mg/Ca), is not primarily explained by glacial-interglacial cyclicity. Combined, these observations are best explained by TEX86 sensitivity to sub-thermocline temperature variability. We conclude that the TEX86 record represents a depth-integrated signal that incorporates a SST and a deeper component, which is compatible the present-day depth distribution of Thaumarchaeota and with the GDGT[2/3] distribution in core tops. The depth-integrated TEX86 record can potentially be used to infer SST variability, because subsurface temperature variability is generally tightly linked to SST variability. Using a subsurface calibration with peak calibration weight between 100–350 m, we estimate that east equatorial Atlantic SST cooled by ~4.5 °C between the Late Miocene and Pleistocene. On shorter timescales, we use the TEX86 record as an Antarctic Intermediate Water (AAIW) proxy and evaluate climatological leads and lags around the Pliocene M2 glacial (~3.3 Ma). Our record, combined with published information, suggests that the M2 glacial was marked by AAIW cooling during an austral summer insolation minimum, and that decreasing CO2 levels were a feedback, not the initiator, of glacial expansion.

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“…Very few taxa across global biodiversity are common (Gaston and Fuller 2007; Gaston 2008; Hannisdal et al 2017), so a large proportion of information is discarded when only common taxa are measured. Fluctuating abundances in rare taxa, that is, those with few individuals and geographically restricted distributions, may prove more ecologically informative, potentially acting as “ecosystem canaries” providing early warning signals for ecosystem collapse (Doncaster et al 2016) and insights into paleoceanographic change (Ishino and Suto 2020) and acting as the focus of conservation efforts (Gaston 2008). However, taxa vary spatially, directly influencing ecological dynamics and diversity patterns within each generation at any single location only (Patzkowsky and Holland 2007).…”

Section: Introductionmentioning

confidence: 99%

Small but mighty: how overlooked small species maintain community structure through middle Eocene climate change

Kearns¹,

Bohaty²,

Edgar³

et al. 2022

Paleobiology

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Understanding current and future biodiversity responses to changing climate is pivotal as anthropogenic climate change continues. This understanding is complicated by the multitude of available metrics to quantify dynamics and by biased sampling protocols. Here, we investigate the impact of sampling protocol strategies using a data-rich fossil record to calculate effective diversity using Hill numbers for the first time on Paleogene planktonic foraminifera. We sample 22,830 individual tests, in two different size classes, across a 7 Myr time slice of the middle Eocene featuring a major transient warming event, the middle Eocene climatic optimum (MECO; ~40 Ma), at study sites in the midlatitude North Atlantic. Using generalized additive models, we investigate community responses to climatic fluctuations. After correcting for any effects of fossil fragmentation, we show a peak in generic diversity in the early and middle stages of the MECO as well as divergent trajectories between the typical size-selected community (>180 μm) and a broader assemblage, including smaller genera (>63 μm). Assemblages featuring smaller genera are more resilient to the climatic fluctuations of the MECO than those assemblages that feature only larger genera, maintaining their community structure at the reference Hill numbers for Shannon's and Simpson's indices. These results raise fundamental questions about how communities respond to climate excursions. In addition, our results emphasize the need to design studies with the aim of collecting the most inclusive data possible to allow detection of community changes and determine which species are likely to dominate future environments.

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Late Pliocene sea-ice expansion and its influence on diatom species turnover in the Southern Ocean

Cited by 6 publications

References 45 publications

A 15-million-year surface- and subsurface-integrated TEX₈₆ temperature record from the eastern equatorial Atlantic

A 15-million-year surface- and subsurface-integrated TEX₈₆ temperature record from the eastern equatorial Atlantic

A fifteen-million-year surface- and subsurface-integrated TEX<sub>86</sub> temperature record from the eastern equatorial Atlantic

Small but mighty: how overlooked small species maintain community structure through middle Eocene climate change

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Late Pliocene sea-ice expansion and its influence on diatom species turnover in the Southern Ocean

Cited by 6 publications

References 45 publications

A 15-million-year surface- and subsurface-integrated TEX86 temperature record from the eastern equatorial Atlantic

A 15-million-year surface- and subsurface-integrated TEX86 temperature record from the eastern equatorial Atlantic

A fifteen-million-year surface- and subsurface-integrated TEX&lt;sub&gt;86&lt;/sub&gt; temperature record from the eastern equatorial Atlantic

Small but mighty: how overlooked small species maintain community structure through middle Eocene climate change

Contact Info

Product

Resources

About

A 15-million-year surface- and subsurface-integrated TEX₈₆ temperature record from the eastern equatorial Atlantic

A 15-million-year surface- and subsurface-integrated TEX₈₆ temperature record from the eastern equatorial Atlantic

A fifteen-million-year surface- and subsurface-integrated TEX<sub>86</sub> temperature record from the eastern equatorial Atlantic