Science - USA (2021-10-29)

biogeography through its close link with ecol-
ogy and ultimately through the varying sen-
sitivity of community size classes to abiotic
and biotic environmental conditions as they
drift along currents.

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ACKNOWLEDGMENTS
We thank O. Jaillon for feedback and help withTaraprojects
coordination; C. de Vargas for feedback and early discussions on
the project; M. Follows and O. Jahn for sharing MITgcm simulation
results for the Arctic Ocean; F. Hartig and O. Maliet for their
guidance on Bayesian inference; L, Arístide and F. Delestro for their
assistance with the figures; C. Fruciano and B. Perez for their
advice on statistics; P. Frémont for his help with environmental
data; B. B. Cael, L. Santoferrara, and an anonymous reviewer for
helpful comments and constructive criticism; and F. Benedetti,
J. Clavel, E. Kazamia, S. Lambert, E. Lewitus, M. Manceau,
O. Missa, S. de Monte, I. Overcast, I. Quintero, E. Ser-Giacomi,
A. C. Silva, and F. Vincent for suggestions and fruitful discussions.
We also thank the commitment and support of the following people
and sponsors: European Molecular Biology Laboratory (EMBL),
Genoscope/CEA, agnès b., Etienne Bourgois, the Veolia
Environment Foundation, Région Bretagne, Lorient Agglomération,
World Courier, Illumina, the Électricité de France (EDF) Foundation,
Fondation pour la recherche sur la biodiversité (FRB), the Prince
Albert II de Monaco Foundation, and theTaraOcean Foundation
and its schooner and teams.Funding:This work was supported by
European Research Council grants (ERC 616419-PANDA to H.M.
and ERC 835067-DIATOMIC to C.B.), grants from the French
Agence Nationale de la Recherche (MEMOLIFE, ref. ANR-10-LABX-

54, to G.S.-K., H.M., and C.B. and OCEANOMICS, ref. ANR-11-BTBR-

0008, to C.B.), funds from the MIUR Italian Flagship project

RITMARE (to D.I.), a grant from the Sakari Alhopuro foundation

(20210172 to G.S.-K.), and funds from CNRS. G.S.-K. received

additional support from the Academy of Finland (decision 328791).

C.B. and H.M. are members of the Research Federation for the

study of Global Ocean Systems Ecology and Evolution (FR2022/

TaraOceans GOSEE). This article is contribution number 124 of

TaraOceans.Author contributions:G.S.-K. and H.M. designed the

study with the help of R.W., D.I., and C.B. G.S.-K. performed the

analyses. R.W. contributed the transport time data and their

interpretation. F.M.I. assisted in the interpretation of 18SrDNA

data. J.J.P.K. provided thepsbOmetagenomic data and their

interpretation. G.S.-K. and H.M. wrote the paper with substantial

input from all co-authors.Competing interests:The authors

declare no competing interests.Data availability:All data

reported here are available without restrictions. Metabarcoding

data have been deposited at the European Nucleotide Archive

under accession numbers PRJEB6610 and PRJEB9737 and

metagenomes under project PRJEB402. Sample metadata are

available from PANGAEA ( 30 ). All code, results and formatted

input data are publicly available from Zenodo ( 31 ).

SUPPLEMENTARY MATERIALS

science.org/doi/10.1126/science.abb3717

Materials and Methods

Supplementary Text

Figs. S1 to S32

Table S1

References ( 32 – 55 )

MDAR Reproducibility Checklist

30 December 2020; accepted 23 September 2021

10.1126/science.abb3717

SEDIMENT TRANSPORT

Exceptional increases in fluvial sediment fluxes

in a warmer and wetter High Mountain Asia

Dongfeng Li^1 *, Xixi Lu^1 *, Irina Overeem^2 , Desmond E. Walling^3 , Jaia Syvitski^2 , Albert J. Kettner^2 ,

Bodo Bookhagen^4 , Yinjun Zhou^5 , Ting Zhang^1

Rivers originating in High Mountain Asia are crucial lifelines for one-third of the world’s population. These

fragile headwaters are now experiencing amplified climate change, glacier melt, and permafrost thaw.

Observational data from 28 headwater basins demonstrate substantial increases in both annual runoff

and annual sediment fluxes across the past six decades. The increases are accelerating from the mid-

1990s in response to a warmer and wetter climate. The total sediment flux from High Mountain Asia is

projected to more than double by 2050 under an extreme climate change scenario. These findings have

far-reaching implications for the region’s hydropower, food, and environmental security.

H

igh Mountain Asia (HMA)—the Tibetan

Plateau and the surrounding high Asian

mountains—is Earth’s third-largest ice

reservoir and the origin of many of Asia’s

large rivers ( 1 – 3 ). Like the polar regions,

HMA is experiencing amplified warming when

compared with general global warming trends

( 4 , 5 ).Theairtemperaturehaswarmedby~2°C

since the 1950s at a much faster rate than the

global average ( 4 ). Precipitation across HMA

has also increased over recent decades, although

the increase is characterized by considerable

spatial heterogeneity ( 6 , 7 ). Existing studies,

based on large-scale cryospheric–hydrological

models, have provided projections for future

increases in the region’s annual runoff due to

climate change ( 3 , 8 ) and their potential im-

pacts on agriculture, food, and ~2 billion people

within HMA and downstream ( 1 , 7 ). One im-

portant potential consequence of these pro-

jected changes in runoff is the possibility of

increased fluvial sediment fluxes across HMA,

which would have important implications for

hydropower generation and development, as

well as water quality, and could affect the en-

ergy, food, and environmental security of the

region ( 2 , 9 , 10 ). Here we investigate the im-

pacts of the changing hydrology on fluvial sedi-

ment fluxes in this region.

We collate and analyze available flow and

sediment load data for rivers in HMA, extend-

ing over the past six decades, to investigate

changes in runoff and sediment flux in re-

sponse to a warmer and wetter climate. To

exclude the potential impact of human activ-

ities, we select 28 quasi-pristine headwater

river basins with observations of both runoff

and sediment flux (plus 14 basins that only

have runoff observations) (table S1). The selec-

tion allows for the separation of climate

change impacts on sediment flux from anthro-

pogenic impacts ( 2 , 11 , 12 ). The dataset has not

yetbeenincludedincurrentglobaldischarge

and sediment datasets ( 2 , 9 , 10 , 13 ). We exam-

ine the sensitivity of sediment flux to changing

temperature and precipitation in HMA on the

basis of observational data and a climate elas-

ticity model (materials and methods). Projec-

tions for future sediment fluxes from HMA are

offered with a qualitative assessment of down-

stream impacts.

SCIENCEscience.org 29 OCTOBER 2021•VOL 374 ISSUE 6567 599

(^1) Department of Geography, National University of Singapore,
Kent Ridge 117570, Singapore.^2 CSDMS, Institute of Arctic
and Alpine Research, University of Colorado Boulder,
Boulder, CO 80309, USA.^3 Department of Geography, College
of Life and Environmental Sciences, University of Exeter,
Exeter EX4 4RJ, UK.^4 Institute of Geosciences, Universität
Potsdam, 14476 Potsdam, Germany.^5 Changjiang River
Scientific Research Institute, Wuhan 430010, China.
*Corresponding author. Email: [email protected] (D.L.);
[email protected] (X.L)
RESEARCH | REPORTS