Takata et al.
Progress in Earth and Planetary Science(2024) 11:30
https://doi.org/10.1186/s40645-024-00633-y

RESEARCH ARTICLE

Progress in Earth andPlanetary Science

Open AccessClimate‑induced shift of deep‑sea benthic
foraminifera at the onset of the mid‑Brunhes
dissolution interval in the northeast tropicalIndian Ocean
Hiroyuki Takata1, Minoru Ikehara2, Koji Seto3, Hirofumi Asahi4, Hyoun Soo Lim5, Sangmin Hyun6 andBoo‑Keun Khim7*   

Abstract
The mid-Brunhes dissolution interval (MBDI; Marine Isotope Stage (MIS) 13 to 7; ~ 533–191 ka) is characterized by vari‑
ous paleoclimatic/paleoceanographic events in the world. We investigated fossil deep-sea benthic foraminifera
and sediment geochemistry at the onset of the MBDI (~ 670–440 ka) using Ocean Drilling Program (ODP) Site 758
and core GPC03 in the northeast tropical Indian Ocean (TIO), primarily focusing on the relationship between the pale‑oceanographic conditions of the surface and deep oceans. Based on multi-dimensional scaling, MDS axis 1 is related
to the specific depth habitats of benthic foraminiferal fauna, possibly at the trophic level. In MDS axis 1, the difference
between the two core sites was smaller from ~ 610 to 560 ka, whereas it was larger from ~ 560 to 480 ka. In contrast,
MDS axis 2 may be related to the low food supply at episodic food pulses/relatively stable and low food fluxes. MDS
axis 2 showed generally similar stratigraphic variations between the two cores during ~ 610–560 ka, but was differ‑
ent during ~ 560–480 ka. The proportion of lithogenic matter to biogenic carbonate was relatively low from ~ 610
to 530 ka under the highstand when sediment transport to the study area was reduced. Thus, both the depth gradi‑
ent in the distribution of benthic foraminiferal fauna and the lithogenic supply between the two cores changed
coincidently across the MIS 15/14 (~ 570–540 ka) transition. Such paleoceanographic conditions across MIS 15/14
transition were attributed to the long-term weakening of the wind-driven mixing of surface waters, which might havebeen caused by the weakening of the Indian summer monsoon in the northeast TIO, possibly with the northward
displacement of the InterTropical Convergence Zone in the Northern Hemisphere. In particular, the depth gradientin the distributions of benthic foraminiferal faunas represents the paleoceanographic linkage between the surface
and deep oceans through particulate organic matter ballasting by calcareous plankton skeletons in addition to litho‑
genic matter, which changed transiently and significantly across MIS 15/14 transition close to the onset of the MBDI.
Keywords Deep-sea biota, Sediment geochemistry, Ballasting effect, Wind-driven mixing, Indian summer monsoon,
InterTropical Convergence Zone

*Correspondence:
Boo‑Keun Khim
bkkhim@pusan.ac.kr
Full list of author information is available at the end of the article© The Author(s) 2024. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which
permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to theoriginal author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images orother third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line
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Takata et al. Progress in Earth and Planetary Science(2024) 11:30

1 Introduction
The duration from Marine Isotope Stage (MIS) 15 to
11 (621–374 ka) is the transitional period between
the mid-Pleistocene Transition (MPT, ~ 1250–700 ka;
Pisias and Moore 1981) and the mid-Brunhes dissolution interval (MBDI) (MIS 13 to 7; ~ 533–191 ka). The
MBDI represents global carbonate dissolution, lasting
several hundred thousand years, centered around MIS 11(~ 424–374 ka; Barth et al. 2018) which is characterizedby paleoceanographic/paleoclimatic events recognized in
the surface and deep oceans (e.g., Jansen et al. 1986; Farrell and Prell 1989). The mid-Brunhes event was defined
as a climatic shift, evidenced by marine sediments andAntarctic ice cores, between MIS 12 and 11 at approximately 430 ka, showing an increase in the amplitude ofglacial-interglacial cycles (EPICA community members
2004). Recently, the mid-Brunhes Transition (MBT) has
been proposed as a two-stage (MBT-1 and MBT-2) global
climate shift and these two stages were distinguished by
global and regional paleoclimatic/paleoceanographic
events (Ao et al. 2020). The first stage (MBT-1) at ~ 500 ka
was generally characterized by the regional phenomenaduring MIS 13 (533–478 ka). In this period, asymmetricaltemperature and precipitation between the hemispheres
and northward displacement of InterTropical Convergence Zone (ITCZ) in the Northern Hemisphere werereported. By contrast, the second stage (MBT-2) at ~ 400
ka was characterized by more global extents of paleoclimatic/paleoceanographic events from MIS 11. Yu et al.
(2017) suggested that MIS 14 (563–533 ka) was uniquelyinterglacial-like, showing more sluggish Atlantic Meridional Ocean Circulation in the North Atlantic, northward shift of the ITCZ, and southward displacement ofwesterlies in the southeastern Pacific. In addition, Barthet al. (2018) suggested several sequential steps of global
climatic events during MIS 15–11. Thus, the transitional
period from MIS 15 to 11 is important in delineating theonset of the MBDI, particularly, focusing on the spatiotemporal variation of paleoclimatic/paleoceanographic
events.
Due to differences in insolation, the sea surface temperature (SST) is relatively high in modern tropical oceans.
The thermal contrast between the tropical and polar
regions is a primary driving force of meridional atmospheric circulation such as the Hadley Circulation (e.g.,
Farrell 1990). In addition, the east–west gradient of the
SST in the tropical ocean often causes interannual variations in atmospheric circulation (i.e., Walker Circulation)such as the El Niño-Southern Oscillation (ENSO) in theequatorial Pacific Ocean (Messie and Chavez 2013). Similar to modern circulation in the high SST tropical oceans(e.g., Fedorov et al. 2015), both the long-term (millionsof years scale order) meridional and zonal atmospheric

Page 2 of 18

circulations might have been present in the geological past. For example, since the middle Pleistocene, thedifferent decreasing SST trend between the eastern
and western equatorial Pacific Ocean has resulted in an
ENSO-like asymmetric zonal pattern along the equator
through the intensity changes of the trade winds (e.g., Lieand Herbert 2004). The eastern tropical Indian Ocean(TIO), located in the Indo-Pacific Warm Pool (IPWP),
plays an important role as a heat source that controls theglobal climate (e.g., De Deckker 2016), revealing that the
spatiotemporal variation of paleoclimatic/paleoceanographic events related to long-term atmospheric circulation change in the TIO during the transitional period(MIS 15–11) is a possible driver of global climatic change.
Because deep-sea biota are sensitive to environmental
conditions, as well as plankton and neritic organism, they
have been used to evaluate the biodiversity of deep-sea
microfossils in response to climatic change (e.g., Yasuhara et al. 2017). Benthic foraminifera provide crucial
information on past trophic conditions (e.g., Gooday
2003; Jorissen et al. 2007). Benthic foraminiferal data
have also been utilized to evaluate the ballasting effectof particulate organic matter (POM) on food delivery to
the seafloor by mineral grains such as plankton skeletons(e.g., Griffith et al. 2021). Takata et al. (2019) studied
the benthic foraminiferal faunas in the central equatorial Pacific Ocean and reported that the shift in the ballasting of POM from calcareous to siliceous plankton
across ~ 300 ka. Takata et al. (2022) investigated thebenthic foraminiferal faunas in the northeast TIO andfound that changes in the ballasting of POM by calcareous plankton skeletons occurred at around 370–210 ka.
Such a paleoceanographic event may be related to a longterm change in the asymmetric zonation of wind-driven
upwelling between the eastern and western TIO, similar
to the modern Indian Ocean Dipole mode (Takata et al.
2024). Since the ballasting of POM by mineral grains is an
important mechanism for linking the paleoceanographic
change between the surface and deep oceans, the ballasting effects of POM can be evaluated by the variation inbenthic foraminiferal fauna in the deep-sea environment,
which implies that atmospheric circulation changes influence the surface ocean conditions.
In this study, we investigated benthic foraminiferal
fauna and measured the major elemental compositions ofbulk sediments in terms of the depth transect at Ocean
Drilling Program (ODP) Site 758 and core GPC03 in thenortheast TIO, adjacent to the IPWP, during MIS 16–12
corresponding to the transitional period between the
MPT and MBDI. The main objective of this study was
to trace the paleoceanographic event at the onset of the
MBDI in the northeast TIO by evaluating the ballasting
effect of POM by mineral grains.

Takata et al. Progress in Earth and Planetary Science(2024) 11:30

2 Methods
Oceanography in the Bay of Bengal is characterized by
the distinct seasonality of wind and precipitation by the
Indian monsoon, and the consequent large amount offreshwater discharge, transporting lithogenic particles
from the Ganga–Brahmaputra–Meghna (GBM) Riversystem. Rixen et al. (2019) observed seasonal variations
in particulate organic carbon (i.e., POM) flux. The summer flux was high at Station SBBT (Southern Bay of Bengal Trap), which is located at a latitude similar to that ofour study area (Fig. 1). In addition, Zhang et al. (2022)
summarized carbonate sedimentation with water depth
in the Indian Ocean, whereas the Bay of Bengal is exceptional area on the relationship between carbonate sedimentation and water depth because of dilution by theabundant lithogenic matter supply from the GBM Riversystem. The Indian summer monsoon is driven by thedifferent heating between the warmer Asian continentand the cooler Indian Ocean with the seasonal movements of the ITCZ (e.g., Webster et al. 1998).
ODP Site 758 (5°21ʹN, 90°21ʹE; water depth 2925m) was drilled at the Ninetyeast Ridge during Leg 121

40˚N

40˚W

0˚

40˚E

80˚E

120˚E

(a)
Site U1446

20˚N
Site 929
0˚

SBBT

(b)

20˚S

40˚S

6˚N

28

00

(b)
0

320

00

38

GPC04
ODP
Site 758

00

36

3400

GPC03

30

5˚N

3800

400

0

3600

3400

00

36

00

3800

4˚N
89˚E

90˚E

Fig. 1 Locality maps of our study area with ODP Site 758 and core
GPC03 ([a] and its close-up [b])Page 3 of 18(Fig. 1). A piston core GPC03 (length 956 cm; 5°20.84ʹN,
88°50.01ʹE; water depth 3650 m) was collected adjacent
to ODP Site 758 in July 2018 during the HI1808 cruise
by R/V ISABU (Fig. 1). Thirty-seven samples were takenfrom 9.9 to 6.3 mbsf (meters below sea floor: 11.7–7.6
mcd [meters composite depth]) at ODP Site 758 HoleA. From core GPC03, thirteen samples were obtained
between 766 and 646 cm. The sediment lithology of both
sampling intervals consisted of mainly calcareous nannofossil ooze (Shipboard Scientific Party 1989; Takata et al.
2022). The sediment samples were freeze-dried for laboratory analyses.
For the faunal analysis of benthic foraminifera, 2–6 gof freeze-dried sediment were processed following theprotocol of Takata et al. (2022). More than 200 benthic
foraminiferal specimens were picked, using a binocular
microscope, in the > 105 µm fraction from split aliquots(1/2 to 1/32) of the washed residues (> 63 µm) that was
followed by Nomura (1995). There are several opinions
about the suitable size fraction and counting number for
faunal analysis of benthic foraminifera (e.g., Boltovskoy
and Wright 1976; Thomas 1985). Some scientists haveadopted the > 150 µm fraction for benthic foraminiferal
fauna, providing convenient identification, whereas otherscientists have stated that the > 63 µm is more useful tocatch the occurrences of the smaller taxa (e.g., phytodetritus species; Thomas 1985). In addition, many scientists
have thought that the 100–300 counts are suitable for the
reliable faunal analysis, as Boltovskoy and Wright (1976)
mentioned. Nonetheless, there are variable ideas on thesuitable size fraction and counting number of benthic
foraminifera. In this study, we adopted the > 105 µm fraction and the 200 counts, following the same scheme ofour previous studies (Takata et al. 2022, 2024). It allows
the combination of the previous results with this study,
which highlights the difference in paleoceanography
between our study period and the younger span. The
specimens were identified, and counted, following taxonomic assignments on Boltovskoy (1978), Corliss (1979),
van Morkhoven et al. (1986), Jones (1994), and Nomura(1995), with the generic classification of Loeblich andTappan (1987). We combined the new 13 data of core
GPC03 with the published 34 data between 841 and595 cm by Takata et al. (2022).
We examined the structure of community for eachsample: rarefaction (diversity E [Sn]; n = 50), Shannon–
Wiener function (Hʹ) (Shannon and Weaver 1949), andthe evenness of Buzas and Gibson (1969). We conducted
non-metric multi-dimensional scaling (MDS) for a data
matrix of relative abundance (25 taxa and 63 samples),following protocol and configuration of Takata et al.
(2022). Calculation of the rarefaction and non-metricmulti-dimensional scaling were performed, using theTakata et al. Progress in Earth and Planetary Science(2024) 11:30

statistical programming environment R (R Development
Core Team 2020) with the function from the Vegan Community ecology package (Oksanen et al. 2019), whereas
Shannon–Wiener function (Hʹ) and the evenness were
calculated via Microsoft Excel software.
For 34 samples from ODP Site 758, the concentrations of 11 major elements (­Na2O, MgO, S­ iO2, ­Al2O3,­P2O5, S, ­K2O, CaO, T­ iO2, MnO, and F­ e2O3) were measured from a briquette, using an energy-dispersive X-ray
fluorescence (XRF) elemental analyzer (MESA-500W,
Horiba Co., Ltd.), following protocols and analyticalconditions of Takata et al. (2024). The weight percentages of the 11 major elements were quantified using thestandard regression method, based on the 12 standards
provided by Dr. H. Fukusawa (former professor at Tokyo
Metropolitan University, Japan). As chlorides were notremoved from the sediment samples by rinsing with distilled water, the ­Na2O data may be slightly overestimated.
In order to objectively evaluate the variations in the
10 elements (except for P­ 2O5), we conducted a R-mode
principal component (PC) analysis using the “prcomp”
function in the statistical programming environment R(R Development Core Team 2020) based on a data matrixof the 10 elements and 33 samples. A sample at 8.48 mcd
of ODP Site 758, which is relatively high S­ iO2 probably
due to one of thin ash layers (Shipboard Scientific Party
1989), was excluded from the principal component analysis. The correlation coefficient was used to calculate thediagonal matrix.
The δ18O and δ13C values of benthic foraminifera(Cibicidoides wuellerstorfi; > 250 µm fraction) from 31
samples of ODP Site 758 were measured at the Marine
Core Research Institute of Kochi University (Japan).
Two to five specimens were analyzed using an Elementar isoprime precisION with the Multicarb preparation system, reacting the samples with 100% phosphoricacid at 90 °C for 10 min. The data were calibrated to the
VPDB standard using IAEA-603 and JCp-1 (Geological Survey of Japan) standards. The analytical precision(± 1σ) was ± 0.16‰ for δ18O and ± 0.13‰ for δ13C. Takata
et al. (2022) reported isotopic data for C. wuellerstorfi incore GPC03. In this study, the isotope values of C. wuellerstorfi (> 250 µm fraction) were additionally measured
for new 13 samples of core GPC03 at the Oregon State
University (USA) following the protocol of Takata et al.
(2022). The analytical precision (± 1σ) was ± 0.02‰ forδ18O and ± 0.04‰ for δ13C.
The orbitally-tuned age models at ODP Site 758 andcore GPC03 were established by oxygen isotope stratigraphy. Isotope data at our study sites were standardized(zero mean and unit variance) prior to their correlation
to global stack LR04 (Lisiecki and Raymo 2005). Stratigraphic correlation was performed under hidden Markov

Page 4 of 18

model (HMM) probabilistic algorithm (Lin et al. 2014;
Ahn et al. 2017). This personal computer-based technique provides age model uncertainties of oxygen isotopealignment from every probabilistic match, as shown in
Fig. 2. The assessments of age model uncertainty at ODP
Site 758 and core GPC03 help heavily on our discussion
on up-downs of mass accumulation rate (MAR).
For ODP Site 758, we calculated the MAR of ­Al2O3
and CaO at ODP Site 758 as follows: A­ l2O3-MAR
or CaO-MAR (g c­m−2 ­kyr−1) = %(Al2O3 or
CaO)/100 × LSR × DBD, where LSR is the linear sedimentation rate (cm k­ yr−1) and DBD is the dry bulk density (g­cm−3) of the sediment. The DBD was obtained from the
Shipboard Scientific Party (1989) by interpolation to ourAge (ka)
7

400

500

600

700

800

(a)
8

Depth
(mcd)

9
10
11
12
500

(b)
600

Depth
(cm)

700
800
900

1000
400

500

600

700

800

Age (ka)
Fig. 2 Age-depth plots at ODP Site 758 (a) and core GPC03 (b).
Dashed lines represent both the upper and lower 95% confidence
rangesTakata et al. Progress in Earth and Planetary Science(2024) 11:30

samples based on core depths (mbsf ) of the same hole
(Hole A). We also calculated the benthic foraminiferal
accumulation rate (BFAR; Herguera and Berger 1991),
following the equation of Herguera and Berger (1991):
BFAR (# c­ m−2 ­kyr−1) = (the number of benthic foraminifera per unit gram of bulk sediment [# ­g−1]) × LSR × DBD.

3 Results
The δ18O and δ13C values of Cibicidoides wuellerstorfi
at ODP Site 758 ranged between 2.7–3.9‰ and − 0.5–
0.4‰, respectively (Table S1; Fig. S1). On the other hand,those of core GPC03 ranged between 2.6–4.6‰ and− 0.9–0.5‰, respectively. Based on the matching of theoxygen isotope profiles to the LR04 stack, the age-depth
curves with 95% confidence intervals for ODP Site 758
and core GPC03 are shown in Fig. 2.
Fossil benthic foraminifera were found in all samples
in this study. The abundances of benthic foraminifera
per unit weight at ODP Site 758 and core GPC03 ranged
from 89 to 301 and 63 to 407, respectively (Fig. 3). Oridorsalis umbonatus, Gyroidinoides sp. A, Pullenia spp.,
Epistominella exigua, Nuttallides umbonifer, and Eilohedra levicula were common constituents in both cores,
auxiliary to Uvigerina dirupta, Siphouvigerina ampullacea, Globocassidulina subglobosa, Cibicidoides mundulus,
and Astrononion echolsi (Figs. 3, 4, 5). Obvious features
on destruction or abrasion of the benthic foraminiferal
tests were not observed both at ODP Site 758 and core
GPC03 (Figs. 4, 5), similar to the observation of Takata
et al. (2022, 2024). These features imply that the faunas
are unlikely to be affected by downward transport fromother areas to the core sites. In addition, severe carbonate
dissolution was not detected on the benthic foraminiferal
tests (Figs. 4, 5).
The faunal associations of benthic foraminifera weregenerally similar between the two cores, whereas sometaxa differed in their stratigraphic distributions between
the cores. For example, the relative abundances of uvigerinids, including Siphouvigerina ampullacea, were morecommon and O. umbonatus was less common at ODP
Site 758 than in core GPC03 (Fig. 3). Both rarefaction­(E[S50]) and Shannon–Wiener (Hʹ) of benthic foraminiferal fauna show frequent fluctuations in ODP Site 758 and
GPC03 (Fig. 6). In addition, the species diversity indicesat ODP Site 758 were partially higher than those of core
GPC03, especially at ~ 630 ka and ~ 490 ka. The evenness
of Buzas and Gibson (1969) was not markedly different
between the two cores but varied significantly with depth(Fig. 6).
Two MDS axes were recognized in the benthic
foraminiferal faunas. The scores of MDS axis 1 at ODP
Site 758 were generally positive, whereas those of core
GPC03 were negative (Fig. 6), suggesting a depth gradient

Page 5 of 18

in the distribution of benthic foraminiferal fauna between
the two cores. The scores of MDS axis 2 showed similarvariation patterns between the two cores during MIS 15,
whereas they showed different variation pattern during
MIS 14–13 (Fig. 6). MDS axis 1 was positively correlatedwith Gyroidinoides sp. A and negatively correlated with
O. umbonatus and Pullenia jarvisi, whereas MDS axis 2
is positively correlated with C. mundulus and negatively
correlated with E. exigua and N. umbonifer (Table S2).
Among the elemental compositions of the bulk sediments at ODP Site 758, ­SiO2 and CaO were the dominant components and ­Al2O3 and ­Fe2O3 were associated(Fig. 7; Table S1). The stratigraphic variation pattern of%CaO was generally opposite to those of %SiO2, %Al2O3,%TiO2, and %Fe2O3 (Fig. 7). According to the principal component analysis, the contributions of PC axes
1, 2, and 3 were 55.9%, 16.1%, and 11.4%, respectively.
Due to the similarly low contributions of PC axes 2 and3, we focused only on PC axis 1 in this study. PC axis 1
was characterized by positive loadings of ­SiO2, ­Al2O3,­TiO2, and ­Fe2O3 and negative loading of CaO (Table 1).
The former combination consists of a common elemental
component in lithogenic matter such as illite and smectite, whereas the latter represents carbonates, particularly
biogenic skeletons. These results suggest that the variation of PC axis 1 depends on the proportion of lithogenic
detrital particles and biogenic carbonates. The PC axis 1scores were normally more positive during MIS 17–16
and MIS 13–12, whereas they were more negative during
MIS 15–14 (Fig. 7). With respect to PC axis 1 loadings,
positive scores represented a greater contribution of lithogenic matter, whereas negative scores symbolized morebiogenic carbonate contributions.

4 Discussion
4.1 Benthic foraminiferal faunas in the northeast tropicalIndian Ocean
4.1.1 Faunal composition

We considered the ecological issues on the two MDS
axes, based on ecological information on modern benthic foraminifera from Supplementary file 5 of Takata
et al. (2022) and the literatures listed in Takata et al.
(2024). Based on the correlation between the score on
MDS axis 1 and the relative abundance of each taxon(Table S2), MDS axis 1 is negatively correlated to Oridorsalis umbonatus and Pullenia jarvisi and positively correlated to Gyroidinoides sp. A. These cosmopolitan taxa
live at various water depths and trophic conditions (e.g.,van Morkhoven et al. 1986). Peterson (1984) reported thespatial distribution of modern benthic foraminifera in theeastern equatorial Indian Ocean. According to his faunal
list, both O. umbonatus and Gyroidinoides orbicularis(likely equivalent to our Gyroidinoides sp. A) are widelyTakata et al. Progress in Earth and Planetary Science

BFN(# g-1)

Epistominella
exigua (%)

Nuttallides
umbonifer (%)(2024) 11:30

Page 6 of 18

mid-Brunhes dissolution interval
MIS 111312
14500
Site 758
400
GPC03
300
200
100
0
40
30
20
10
0
15

15

16

17

650

700

10
5
0
15

Eilohedra
levicula (%)

10
5
0
15

Globocassidulina
subglobosa (%)

10
5

0
25
Uvigerina spp. + 20
15
Siphouvigerina
10
ampllacea (%)
5
0
25
20
15
Oridorsalis
umbonatus (%) 10
5
0
25
20
15
Gyroidinoides
10
spp. (%)
5
030
Pullenia
spp. (%)

20
10
0
10

Astrononion
echolsi (%)

5
0

400

450

500

550
600
Age (ka)

Fig. 3 Occurrences of benthic foraminifera. The abundance of benthic foraminifera per unit weight (BFN) and relative abundances of selected
species of benthic foraminifera at ODP Site 758 (orange line) and core GPC03 (blue line) were shownTakata et al. Progress in Earth and Planetary Science(2024) 11:30

Page 7 of 18

Fig. 4 Scanning electron micrographs of selected benthic foraminifera from ODP Site 758. Scale bars are 100 µm. 1a, b. Uvigerina dirupta
from sample 758A-2H2-22-24 cm; 2a,b. Siphouvigerina ampullacea from sample 758A-2H1-92-95 cm; 3. Globocassidulina subglobosa from sample
758A-2H2-35-37 cm; 4a-c. Epistominella exigua from sample 758A-2H1-136-138 cm; 5a-c. Nuttallides umbonifer from sample 758A-2H1-113-116
cm; 6a-c. Oridorsalis umbonatus from sample 758A-2H2-48-50 cm; 7a-c. Gyroidinoides sp. A from sample 758A-2H1-113-116 cm; 8a-c. Cibicidoides
mundulus from sample 758A-2H2-44-47 cm; 9a, b. Pullenia bulloides from sample 758A-2H2-40-42 cm; 10a, b. Pullenia jarvisi from sample
758A-2H2-22-24 cm; 11a-c. Eilohedra levicula from sample 758A-2H2-44-47 cm; 12a, b. Astrononion echolsi from sample 758A-2H2-29-32 cm

common at water depth of ~ 2000–4600 m, which cover
the sampling water depths of our study sites (2925 m at
ODP Site 758 and 3650 m at core GPC03). In the present study, the relative abundance of O. umbonatus wascommon during MIS 17–11 (Fig. 3). Takata et al. (2022)
reported that its occurrence generally decreases after
MIS 11. Thus, the past habitats of these species might
have been different during MIS 16–12 compared to theirmodern distributions. It may be difficult to specify theexact reason for their different occurrences during MIS
16–12 in the two cores, just based on modern ecological knowledge. In contrast, Siphouvigerina ampullacea
was slightly positively correlated with MDS axis 1 (0.46)(Table S2). Other Uvigerina spp. were also more common
at ODP Site 758 than at core GPC03 (Fig. 3). Uvigerinids
are usually regarded as eutrophic taxa (e.g., Jorissen et al.
1997). Hence, although the interpretation of the ecological issue of MDS axis 1 is still difficult, the negative score

Takata et al. Progress in Earth and Planetary Science(2024) 11:30

Page 8 of 18

Fig. 5 Light micrographs of selected benthic foraminifera from ODP Site 758. Scale bars are 100 µm. 1a, b. Uvigerina dirupta from sample
758A-2H2-22-24 cm; 2a,b. Siphouvigerina ampullacea from sample 758A-2H1-92-95 cm; 3. Globocassidulina subglobosa from sample 758A-2H2-35-37
cm; 4a-c. Epistominella exigua from sample 758A-2H1-136-138 cm; 5a-c. Nuttallides umbonifer from sample 758A-2H1-113-116 cm; 6a-c. Oridorsalis
umbonatus from sample 758A-2H2-48-50 cm; 7a-c. Gyroidinoides sp. A from sample 758A-2H1-113-116 cm; 8a-c. Cibicidoides mundulus from sample
758A-2H2-44-47 cm; 9a, b. Pullenia bulloides from sample 758A-2H2-40-42 cm; 10a, b. Pullenia jarvisi from sample 758A-2H2-22-24 cm

on MDS axis 1 was related to deeper water habitats ofbenthic foraminiferal fauna, especially at deep site (core
GPC03) during MIS 16–12, whereas a positive score wasrelated to shallower water habitats possibly with a relatively higher food supply.

MDS axis 2 was negatively correlated with
Epistominella exigua and Nuttallides umbonifer andpositively correlated with Cibicidoides mundulus(Table S2). Epistominella exigua is known as a common
species with an episodic food supply (Gooday 1994;

Takata et al. Progress in Earth and Planetary Science(2024) 11:30

Page 9 of 18

mid-Brunhes dissolution interval
MIS 11
13
12
14
400
300
BFAR
(# cm-2 kr-1) 200
100
0

15

16

17

Site 758
GPC03

25
E (S50)

20
15

ShannonWiener (H’)

3
2.5
0.7

Evenness

0.6
0.5

MDS
axis 1

0.4
0.4
0.2
0
-0.2
-0.4
0.3

MDS
axis 2

0
-0.3

400

450

500

550
Age (ka)

600

650

700

Fig. 6 Stratigraphic variations of benthic foraminiferal accumulation rate (BFAR) and the structure of the community, and multi-dimensional scaling.
Rarefaction ­(E[S50]), Shannon–Wiener index (Hʹ) evenness of Buzas and Gibson (1969), and scores of MDS axis 1 and 2 at ODP Site 758 (orange line)
and core GPC03 (blue line) were shownTakata et al. Progress in Earth and Planetary Science(2024) 11:30

Page 10 of 18

mid-Brunhes dissolution interval
MIS 11
6
4
2
PC axis 1 0
-2
-4
-6
50

12

13

14

15

16

17

550

600

650

700

56.75%

45
SiO2 (%)

40
35
10
8

Al2O3 (%)

6
2

2.89%

K2O (%)1
0.24
TiO2 (%) 0.23
0.22
3
Fe2O3 (%)

2

CaO (%)

1
45
40
35
30
25
400

8.78%

450

500

Age (ka)
Fig. 7 Stratigraphic variations of PC axis 1 and selected 7 major elements at ODP Site 758

Takata et al. Progress in Earth and Planetary Science(2024) 11:30

Page 11 of 18

Table 1 Loadings of ten elements for PC axis 1 at ODP site 758
Element

Na2O

MgO

Al2O3

SiO2

S

K2O

CaO

TiO2

MnO

Fe2O3

PC axis 1− 0.22

0.62

0.98

0.93

0.30

0.85

− 0.94

0.94

0.15

0.87

Smart et al. 1994; Thomas et al. 1995; Thomas andGooday 1996; Sun et al. 2006; Thomas 2007; Takata
et al. 2016). Many studies have reported that Nuttallides umbonifer occurred at abyssal depths between
the lysocline and the calcium carbonate compensation depth (CCD) (Bremer and Lohmann 1982; Mackensen et al. 1990, 1993, 1995; Schmiedl et al. 1997).
This species also tolerates an extremely low food supply (Schmiedl et al. 1997) in the greater depths where
the organic matter reaches only a very small portion
from surface ocean to the seafloor in general (Martin
et al. 1987; Rigwell 2003; Henson et al. 2012; Griffith
et al. 2021). Nuttallides rugosa (probably equivalent toN. umbonifer) was reported at ~ 1916 m water depthof the western Arabian Sea (Kurbjeweit et al. 2000).
However, this species is commonly associated with low
and seasonal food supplies (Gooday 1994, 2003; Sunet al. 2006), possibly due to its tendency to reproduce
in such season. De and Gupta (2010) found N. umbonifera and E. exigua at the abyssal depths of the eastern and central Indian Ocean, which is characterizedby carbonate-corrosive cold bottom waters and a low
and pulsed food supply. However, C. mundulus is common under oligotrophic conditions (e.g., van Morkhoven et al. 1986), probably with a non-episodic (i.e.,
relatively stable) food supply, compared to E. exigua.
Thus, a negative score on MDS axis 2 is likely related
to an extremely low food supply with episodic foodpulses, whereas a positive score may indicate a low but
relatively stable food supply.
In summary, during our study period (MIS 16–12),
MDS axis 1 was related to the specific depth habitats
of benthic foraminiferal faunas possibly with trophic
conditions in the tropical Indian Ocean, whereas MDS
axis 2 may be related to food supply conditions. Thus,
benthic foraminiferal fauna during MIS 16–12 seemed
to be mainly influenced by water depth and episodic
states of the food supply from the surface waters.

4.1.2 Depth gradient in the distributions of benthic
foraminiferal faunas

Rarefaction ­(E[S50]) and the Shannon–Wiener index (Hʹ)
at ODP Site 758 decreased slightly from late MIS 14 toearly MIS 13, whereas those of core GPC03 did not vary
distinctly (Fig. 6). The long-term changes in the species diversity of benthic foraminifera differed between
the two sites. This suggests that the long-term changes
in species diversity of benthic foraminifera occurred
mainly at the shallow site (ODP Site 758; 2925 m water
depth) rather than at the deep site (GPC03; 3650 m water
depth). The difference in MDS axis 1 between the twocores was generally large during glacial periods (MIS 16
and 14; Fig. 8). In particular, MDS axis 1 during MIS 15
was similar, whereas that during MIS 14–13 was different(Fig. 6). Thus, the large difference in MDS axis 1 between
the two cores seems to indicate an increased depth gradient in the distribution of benthic foraminiferal fauna. In
contrast, MDS axis 2 showed a generally similar patternof variation (small variation in the difference in MDS axis
2 in Fig. 8) between the two cores before MIS 15 (Fig. 6),
whereas it was different (large variation in the differencein MDS axis 2 in Fig. 8) during MIS 14–13 (Fig. 6). Thus,
based on both the structure of the community and thefaunal composition represented by MDS axis 1, the depth
gradient in the distribution of benthic foraminiferal faunas between ODP Site 758 and core GPC03 increased
during MIS 14–13.
The lateral distance between ODP Site 758 and core
GPC03, located at ~ 5ºN is quite short (~ 168 km).
Although we cannot dismiss the possibility of lateral
distance on the oceanographic difference, it is reasonable to assume that the depth gradient in the distributionof benthic foraminiferal faunas seems to result fromdifferent water depths (~ 730 m difference) between thetwo sites. Such a depth gradient in the distribution ofbenthic foraminiferal faunas is difficult to comprehensively interpret based on modern ecological knowledge.
However, this may be partly explained by the changes(See figure on next page.)
Fig. 8 Stratigraphic variations of the several indices in this study. Mass accumulation rate (MAR) of CaO and ­Al2O3 and benthic foraminiferal
accumulation rate (BFAR), sea-level change (Spratt and Lisiecki 2016), the differences of the scores of MDS axis 1 and 2 between ODP Site 758
and core GPC03, the relative abundance of Globigerina bulloides at ODP Site 758 (Chen and Farrell 1991), and relative abundance of G. bulloides(Bhadra and Saraswat 2022) and stable oxygen isotope variations of seawater that was estimated by oxygen isotope values of planktonic
foraminifera and TEX 86-sea surface temperature at IODP Site U1446 (Clemens et al. 2021) were shownTakata et al. Progress in Earth and Planetary Science(2024) 11:30

mid-Brunhes dissolution interval
MIS 11
13
12
14
0.8
Al2O3
MAR
0.6
CaO
(g cm-2 kr-1)(Site 758) 0.4
0.2
0
6
4
2
PC axis 1
0(Site 758)
-2
-4
-6

Page 12 of 18

15

16
BFAR

17

400
BFAR
300
(# 102 cm-2 kr-1)
200 (Site 758)10000Sea-level
(m)

-50
-100

0.4
0.3
Difference of
MDS axis 1 0.2(Site 758) 0.1
00.3
Difference of
MDS axis 2(Site 758)

mean = 0.17

0mean = -0.05-0.3
15
Globigerina 10
bulloides (%)
5(Site 758)
030
Globigerina 20
bulloides (%) 10(Site U1446)
0-1
δ18Osw (‰)(Site U1446)

0
1
400

Fig. 8 (See legend on previous page.)

450

500

550
600
Age (ka)

650

700

Takata et al. Progress in Earth and Planetary Science(2024) 11:30

in water mass during the MIS 16–12. Peterson and Prell(1985) reported that the Composite Dissolution Index(CDI) was more negative (i.e., more carbonate-corrosive condition) in the equatorial Indian Ocean during
MIS 13–11. The boundary between the Indian Deep
Water (IDW) and Indian Bottom Water (IBW) is currently roughly consistent with the lysocline (~ 3900–
3800 m water depth) at present (Peterson 1984) where
the CDI is almost 0 (Peterson and Prell 1985). Thus,
during MIS 13–12, the boundary between the IDW
and the IBW might be located shallower than the core
GPC03 site (3650 m water depth), compared to the present day. Thus, the depth gradient in the distribution ofbenthic foraminiferal faunas between ODP Site 758 andcore GPC03 was enhanced during MIS 13–12.
Howe and Piotrowski (2003) reported stratigraphic
changes in εNd at ODP Site 929 (western equatorial
Atlantic) over the last ~ 800 ka (Fig. S2). The εNd value in
the Atlantic Ocean represents the proportion of AABW
to NADW. This fluctuation in εNd clearly indicates theorbital-scale glacial-interglacial variations, similar to
LR04 stack of benthic δ18O values (Lisiecki and Raymo2005). However, they did not show a marked long-term
tendency during the MBDI. On the other hand, Barthet al. (2018) reported a larger gradient of benthic Δδ13C
values between the North Atlantic and South Atlantic
during the “pre-MBT (mid-Brunhes Transition)” than“post-MBT” (Fig. S2). They regarded the larger gradient of benthic Δδ13C values as the northward penetration of AABW and the lower gradient as the southward
penetration of NADW. They recognized that the gradient of benthic Δδ13C values between the North Atlantic
and South Atlantic changed at the beginning of MIS 12(~ 436 ka), and this transition appears to be a gradualchange during MIS 14–12 than an abrupt one (Fig.
S2). This onset timing is generally consistent with ourobservation of an enhanced depth gradient of the MDS
axes across MIS 14. Although careful interpretationis necessary, based on the Δδ13C values between the
North Atlantic and South Atlantic which indicate thedifferent proportion of deep-water formation between
the AABW and NADW, the enhanced depth gradient in
the distribution of benthic foraminifera across MIS 14
might be related to the global deep-water circulation.
In summary, the specific depth distribution of benthic
foraminifera represented by MDS axis 1 between ODP
Site 758 and core GPC03 seems to be related to theshallower position of the boundary between the IDW
and IBW in the Indian Ocean during MIS 16–12, compared to the modern ocean. In addition, changes in thedepth distribution of benthic foraminifera across MIS
14 may reflect changes in global deep-water circulation.

Page 13 of 18

4.2 Ballasting effect of particulate organic matterby mineral grain in the northeast tropical Indian Oceanprior to the onset of the mid‑Brunhes dissolution
interval

Sediment trap studies have reported the ballasting effectof particulate organic matter (POM) by mineral grains in
the water columns of modern ocean (Francois et al. 2002;
Henson et al. 2012; Rixen et al. 2019). Ballasting of POM
by biogenic carbonate grains (calcareous plankton skeleton) may increase the transfer efficiency of POM fromthe surface waters to the seafloor (Francois et al. 2002).
Benthic foraminiferal data have been used to evaluate
the ballasting effects of POM by mineral grains (DiesterHaass and Faul 2019; Griffith et al. 2021; Takata et al.
2019, 2022). Takata et al. (2022) reported a positive correlation between BFAR and carbonate-MAR in core GPC03
from ~ 600–370 ka (MIS 15–11) and after ~ 210 ka (midMIS 7), which suggests that calcareous plankton skeletons (probably mainly calcareous nanoplankton) affected
the transfer efficiency of POM through the ballasting
effect of POM in the northeast TIO. In our study interval (MIS 16–12), the correlation between the BFAR and
CaO-MAR was positive (r = 0.66, P < 0.01) at ODP Site
758 (Fig. 8). Since the contribution of Ca-bearing silicates(e.g., illite) was very minor compared to biogenic carbonate (Takata et al. 2022), the positive correlation implies
that calcareous plankton skeletons seem to promote thebetter transfer of sinking POM in the water column as
ballast at ODP Site 758 during our study period (MIS
16–12).
In our study area, lithogenic matter was affected mainly
by riverine input from the GBM Rivers (e.g., Zhang et al.
2022). In addition to calcareous plankton skeletons,
lithogenic matter is thought to be an efficient ballasting material for POM sinking (Rixen et al. 2019). Takata
et al. (2024) reported a positive correlation between %N.
umbonifer and the contribution of lithogenic matter during the last ~ 450 ka, confirming the increasing ballasting effect of POM by lithogenic matter in the northeast
TIO. At ODP Site 758, the correlation between BFAR
and ­Al2O3-MAR was positive (r = 0.79, P < 0.01) during MIS 16–12 (Fig. 8). In addition to calcareous plankton skeletons, lithogenic matter such as illite-containing
aluminum seemed to intensify the transfer efficiency ofsinking POM in the water column as ballast at ODP Site
758 during MIS 16–12. Particularly, during MIS 15–14,
PC axis 1 on the major elemental compositions related
to lithogenic matter and biogenic carbonate was largely
negative (Fig. 8), suggesting that the contribution oflithogenic matter was relatively low, compared to biogenic carbonate. Because this period is characterized bya relatively high sea level (Spratt and Lisieki 2016; Fig. 8),
the low contribution of lithogenic matter is due to theTakata et al. Progress in Earth and Planetary Science(2024) 11:30

distance from the mouths of the GBM Rivers to our study
area.
The variation in PC axis 1 of the major elemental compositions showed short-term fluctuations during MIS 15(Fig. 8). The timing of the negative scores of PC axis 1 inthis period generally corresponded to relatively high sea
levels at ~ 610, ~ 590, and ~ 570 ka (Fig. 8). In addition,
the scores of MDS axis 2 of benthic foraminifera weremore positive and increased twice at ~ 590 ka and ~ 570
ka at both ODP Site 758 and core GPC03 (Fig. 6). It isreasonable to suppose that the small fluctuations of lithogenic matter supply may have resulted in more shortterm positive scores on MDS axis 2 at both cores under
the decreasing supply of lithogenic matter during MIS 15
due to the highstand. This low supply of lithogenic matter
during MIS 15 may be attributed to frequent fluctuationsin the episodic/more stable food supply from the surface
waters to the seafloor.
The greater influence of lithogenic matter during MIS
14–13 may also explain the different variation patternsof MDS axis 2 between ODP Site 758 and core GPC03(Fig. 8) through the efficiency of sinking POM in thewater column. A shift to different variation patterns of
the scores of MDS axis 2 between the two cores during
MIS 14–13 implies that the food supply became more
episodic (e.g., more seasonal variation) at the shallower
site (ODP Site 758) than at the deeper site (core GPC03)(Fig. 8). The faunal transition from MIS 15 to MIS 14–13
may be attributed to the change from a more stable foodsupply to a more episodic food supply from the surface
waters.
However, the relationship between PC axis 1 and %N.
umbonifer at ODP Site 758 (Fig. 2) was not strong during our study period (MIS 16–12), compared with theyounger interval (MIS 10–1) in core GPC04 which islocated close to ODP Site 758 (Takata et al. 2024). The
mode of the ballasting effect of POM by lithogenic matter in our study area seemed to differ between MIS 16–12
and the younger period (MIS 8–1). Thus, this seems to
support the inference of Takata et al. (2024) that the
influence of riverine lithogenic matter supply became
significant for the vertical transportation of POM in ourstudy area due to increased sea level lowering during glacial periods since MIS 8.
4.3 Paleoceanography in the northeast tropical Indian
Ocean at the onset of the mid‑Brunhes dissolution
interval

Chen and Farrell (1991) reported planktonic foraminiferal fauna during the last ~ 800 ka at ODP Site 758(Fig. 8). According to their faunal data, the %Globigerina
bulloides declined across MIS 14, despite the possible
severe carbonate dissolution to planktonic foraminiferal

Page 14 of 18

fauna during MIS 15–14. This species is common in the
upwelling regions of low-latitude oceans (e.g., Thiede1975). Maeda et al. (2022) conducted a sediment trap
study at Station CBBT-N (southwestern Bay of Bengal)
and reported that G. bulloides was common during themonsoon periods (summer and winter) owing to theenhanced surface and subsurface primary production.
This ecological evidence suggests that the decline of %G.
bulloides at ODP Site 758 is related to decreased primary
production due to the weakening of wind-driven mixing
in the surface waters of the northeast TIO across MIS
15/14 transition. In contrast, Bhadra and Saraswat (2022)
reported that %G. bulloides declined during MIS 14 at
IODP Site U1446 (northern Bay of Bengal; 1441 m water
depth), similar to ODP Site 758 (Fig. 8), despite highamplitude short-term variations. They interpreted thatthe long-term declining trend of this species across MIS
14 was related to Indian summer monsoon variability. In
addition, the estimated δ18O values of seawater increased
generally from MIS 15 to MIS 13, confirming the weakening of the Indian summer monsoon (Fig. 8; Clemens
et al. 2021). Thus, the long-term declines of %G. bulloides
at both IODP Site 1446 and ODP Site 758 in the Bay of
Bengal suggests that the weakening of the Indian summer monsoon occurred in our study area across the MIS
15/14 transition, which might have caused the long-term
weakening of wind-driven mixing in the surface ocean.
Across MIS 15/14 transition, changes in PC axis 1 (theproportion of lithogenic matter to biogenic carbonate)
at ODP Site 758 and the depth differences in MDS axes
1 and 2 (benthic foraminiferal faunas) between ODP
Site 758 and core GPC03 were observed (Fig. 8). Bothchanges between surface water oceanography (i.e., foodproduction) and deep-sea biota (i.e., benthic foraminifera) were altered temporally and significantly across MIS
15/14 transition, possibly through the ballasting effect of
POM by calcareous plankton skeletons and the lithogenic
matter. Yu et al. (2017) reported that the “interglacial-likeMIS 14” was a unique paleoceanographic setting, suchas more sluggish Atlantic Meridional Ocean Circulation, and the northward shift in the ITCZ in the Northern Hemisphere. The weakening of the Indian summer
monsoon across MIS 15/14 transition also seems be thepaleoceanographic condition of “interglacial-like MIS
14” in the northeast TIO. The northward displacement of
the ITCZ during MIS 13 (MBT-1) proposed by Ao et al.
(2020) may also be related to the weakening of the Indiansummer monsoon and subsequent faunal transition of
deep-sea benthic foraminiferal in the northeast TIO
across MIS 14. The weakening of the wind-driven mixing
with the Indian summer monsoon is usually related tomore southward seasonal movement of the ITCZ at thepresent day. On the other hand, the long-term weakening

Takata et al. Progress in Earth and Planetary Science(2024) 11:30

of the wind-driven mixing in the northeast TIO with
the Indian summer monsoon (as shown by G. bulloides
at ODP Site 758 and IODP Site 1446) across MIS 15 to
13 transition seemed to be related to the global climaticchange resulting from the asymmetric climatic variations
between the Northern and Southern Hemispheres acrossMIS 14 (e.g., Hao et al. 2015). During this period, Ao
et al. (2020) reported the northward displacement of the
ITCZ in the Northern Hemisphere.
Yu et al. (2017) proposed the two hypotheses for theunique paleoceanographic setting of “interglacial-likeMIS 14.” The first hypothesis concerns on the influenceof more nutrient-rich cold water from high latitudes via
the Peru–Chile Current in the eastern equatorial Pacific(EEP). In addition, the magnitude of the EEP cold tongue
weakened in the EEP through the atmospheric bridge ofa northward ITCZ shift and the resulting heat/moisturetransport across the eastern equatorial Atlantic (EEA).
Another hypothesis is that the unique orbital variations
in MIS 14 that were characterized by higher obliquity
fluctuations and lower eccentricity/precession, resulting
in an inter-hemispheric asymmetry. Both hypotheses canbe applied to the northeast TIO to change the surface
water oceanography and deep-sea benthic foraminiferal
fauna.
Barth et al. (2018) summarized the multi-proxy dataof multiple core sites in the world’s ocean from thelast ~ 800 ka by conducting principal component analyses. More positive excursion of δ13C values of benthic
foraminifera was distinct during MIS 13 (their PC axis
1 in Figs. 6 and 7). Such positive δ13C excursion is significant in the Atlantic Ocean, but it is not obvious in the
Pacific Ocean. More positive shift was not also distinct
in our δ13C values of C. wuellerstorfi in core GPC03 (Fig.
S2). More positive excursion of δ13C values of benthic
foraminifera during MIS 13 was attributed to the uniquesetting of export productivity between the Antarctic zone
and Subantarctic zone in the Southern Ocean (as shownin Fig. 9 of Barth et al. 2018). Barth et al. (2018) suggested
that, during MIS 15–13, a build-up of Northern Hemisphere biomass as a result of accumulation of isotopically light carbon and enriched 13C in the ocean due toAsian summer monsoon. In the Bay of Bengal, both %G.
bulloides and estimated δ18O values of seawater at IODP
Site 1446 (Bhadra and Saraswat 2022; Clemens et al.
2021) imply stronger Indian summer monsoon during
MIS 15 to 13 (Fig. 8), although their interpretation waspartly inconsistent to the weakening of the Indian summer monsoon across MIS 15/14 transition in our study
area. Further data evaluation of the Asian summer monsoon during MIS 15–13 is necessary to confirm Barthet al. (2018), who proposed sequential steps of paleoceanographic events related to the carbon cycle during

Page 15 of 18

the MBDI. Finally, Takata et al. (2024) suggested that thebenthic foraminiferal fauna in the northeast TIO could
have been influenced by the Indian Ocean Dipole modelike long-term transition during late MIS 9–8, following
the scheme of Gupta et al. (2010). Similar paleoceanographic events may have affected the long-term changes
in surface- and deep-sea conditions in the northeast TIO
at the onset of the MBDI.

5 Conclusions
This study investigated fossil benthic foraminifera andsediment geochemistry at ODP Site 758 and core GPC03
in the northeast tropical Indian Ocean during MIS 16–12
and led to the following conclusions:
1. MDS axis 1 is related to the specific depth habitats
of benthic foraminiferal fauna, possibly to the trophic
condition in the TIO during MIS 16–12. The difference in MDS axis 1 between the two sites was
smaller during MIS 15, but it was larger during MIS
14–13 because of the depth gradient in the distributions of benthic foraminiferal faunas. MDS axis 2
may be related to the low food supply with episodic
food pulses/relatively stable low food flux. The variation pattern of this axis was generally similar during
MIS 15 between the two cores but different during
MIS 14–13. This indicates that the depth gradient
between these two cores was intensified during MIS
14–13, which may be attributed to the shoaling
boundary between the Indian Deep Water and Indian
Bottom Water. Such a paleoceanographic event
might be related to deep-water circulation changes in
the Atlantic Ocean during the same period.
2. During the highstand across MIS 15/14 transition,changes in the proportion of lithogenic matter tobiogenic carbonate represented by PC axis 1 at ODP
Site 758 and the depth gradient in the distributionsof benthic foraminiferal fauna between ODP Site
758 and core GPC03 were discernible. During such
paleoceanographic events, the linkage between thesurface and deep oceans was altered temporally andsignificantly, particularly across MIS 15/14 transition,
mainly due to the ballasting effect of POM by calcareous plankton skeletons in addition to lithogenic
matter.
3. The decrease of %Globigerina bulloides across MIS
15/14 transition represents the reduced primary
production due to the weakening of wind-driven
mixing in the surface ocean in our study area. Suchpaleoceanographic condition has been attributed to
the long-term weakening of the wind-driven mixing
in the northeast TIO with the Indian summer monsoon, possibly due to the northward displacement of

Takata et al. Progress in Earth and Planetary Science(2024) 11:30

the InterTropical Convergence Zone across MIS15
to 13. The long-term weakening of the Indian summer monsoon across MIS 15/14 enhanced the depth
gradient in the distribution of benthic foraminifera in
the northeast TIO.
Abbreviations
AABW	Antarctic Bottom Water
BFAR	Benthic foraminiferal accumulation rate
CDI	Composite Dissolution Index
ENSO	El Niño-Southern Oscillation
GBM	Ganga–Brahmaputra–Meghna
IBW	Indian Bottom Water
IDW	Indian Deep Water
IODP	International Ocean Discovery Program
ITCZ	InterTropical Convergence Zone
MAR	Mass accumulation rate
MBDI	Mid-Brunhes dissolution interval
MBT	Mid-Brunhes Transition
MDS	Multi-Dimensional Scaling
MIS	Marine Isotope Stage
NADW	North Atlantic Deep Water
ODP	Ocean Drilling Program
POM	Particulate organic matter
SSBT	Southern Bay of Bengal Trap Station
SST	Sea surface temperature
TIO	Tropical Indian Ocean

Supplementary Information
The online version contains supplementary material available at https://​doi.​
org/​10.​1186/​s40645-​024-​00633-y.
Supplementary Material 1: Figure S1. Isotope stratigraphy in our study at
ODP Site 758 and in core GPC03.
Supplementary Material 2: Figure S2. Stratigraphic variations of several
proxy data in this study. Carbon isotope values of Cibicidoides wuellerstorfi
in core GPC03, εNd at ODP Site 929 (Howe and Piotrowski 2003), and Δδ13C
values between the North and South Atlantic Ocean (Barth et al. 2018)
were shown.
Supplementary Material 3: Table S1. Weight percent of 11 major elements,
score of PC axis 1, and stable oxygen and carbon isotope ratios of Cibicidoides wuellerstorfi at ODP Site 758
Supplementary Material 4: Table S2. Occurrences of fossil benthic
foraminifera at ODP Site 758
Supplementary Material 5: Table S3. Correlation coefficient between MDS
axes and each taxon; the results between MDS axis 1 or 2 and each taxon
at ODP Site 758 and core GPC03
Acknowledgements
We thank Yusuke Kubo and curation staffs of Kochi Institute for Core Sample
Research for their support to sampling of ODP Site 758. We are indebted to
Library of Marine Samples, Korea Institute of Ocean Science and Technol‑ogy (KIOST) for their support to sampling of core GPC03. We appreciatetechnicians of Marine Core Research Institute (Kochi University) for theirsupport to stable isotope analysis of ODP Site 758. We are also indebted to
Akita Tsujimoto (Shimane University), Takuya Sagawa, and Robert G. Jenkins(Kanazawa University) for their help to take light and SEM micrographs of ben‑thic foraminifera. We also thank Li Lo (handling editor) and two anonymous
reviewers for their constructive comments to improve the manuscript. This
research used samples and/or data provided by the Ocean Drilling Program(ODP) that is sponsored by the U.S. National Science Foundation (NSF) andparticipating countries under management of Joint Oceanographic Institution(JOI), Inc.

Page 16 of 18

Author contributions
HT is responsible for conducting the faunal analysis of benthic foraminifera
of ODP Site 758 and core GPC03 and for writing the manuscript. MI and SH
conducted stable isotope analyses for ODP Site 758 and core GPC03, respec‑tively. KS conducts XRF analysis with HT. HA is responsible for constructing theage models for ODP Site 758 and core GPC03. HSL contributes to shape themanuscript. BKK designed this research and is responsible for aiding to write
the manuscript and managing the discussion for consensus. All authors agree
to submission of the manuscript.
Funding
This work was supported by BK21 FOUR Program of Pusan National University,
the National Research Foundation of Korea (2022R1A2B5B01001811), Korea
Institute of Marine Science & Technology funded by the Ministry of Oceans
and Fisheries (RS-2023-00256330), and the Korea Institute of Ocean Scienceand Technology (KIOST) research program (PEA0182).
Availability of data and materials
The datasets supporting the conclusions of this article are included within its
additional files.

Declarations
Competing interests
The authors declare that they have no competing interest.
Author details
1
BK21 School of Earth and Environmental Systems, Pusan National University,
2 Busandaehak‑ro 63 beon‑gil, Busan 46241, Republic of Korea. 2 Marine Core
Research Institute, Kochi University, B200 Monobe, Nankoku 783‑8502, Japan.
3
Estuary Research Center, Shimane University, 1060 Nishikawatsu, Mat‑sue 690‑8504, Japan. 4 Fukui Prefectural Satoyama-Satoumi Research Institute,122‑12‑1 Torihama, Wakasa 919‑1331, Japan. 5 Department of Geological Sci‑
ences, Pusan National University, 2 Busandaehak‑ro 63 beon‑gil, Busan 46241,
Republic of Korea. 6 Marine Environmental Research Department, Korea
Institute of Ocean Science and Technology, 385 Haeyang‑Ro, Busan 49111,
Republic of Korea. 7 Department of Oceanography and Marine Research Insti‑tute, Pusan National University, 2 Busandaehak‑ro 63 beon‑gil, Busan 46241,
Republic of Korea.
Received: 12 November 2023 Accepted: 22 May 2024

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