Gong et al. (2022) Of Atlantic Meridional Overturning Circulation in the CMIP6 Project

X. Gong, H. Liu, F. Wang, and C. Heuzé (2022). Of Atlantic Meridional Overturning Circulation in the CMIP6 Project. Deep Sea Research Part II: Topical Studies in Oceanography, p.105193, doi: 10.1016/j.dsr2.2022.105193

The Atlantic Meridional Overturning Circulation or AMOC is one of the most famous climate tipping points, even mentioned in disaster movies. But its future is still uncertain, as climate models do not represent it as accurately as we wished.

In this publication, we computed the mean state and variabilities of the AMOC in the latest generation of global climate models used by the IPCC, a.k.a. CMIP6 models, and determine whether the representation of the AMOC has improved since CMIP5. The answer is: it depends…

The CMIP6 models disagree regarding the sign of the current trend in the AMOC, with several even saying that there is no trend. Adapted from Fig.6 of Gong et a. (2022).

The models agree more with each other in terms of AMOC value now in CMIP6 than they did in CMIP5, but disagree when it comes to the variability. More worryingly, while most CMIP5 models had the AMOC weakening currently, CMIP6 models now diverge: half say it weakens, and half say it does not or even increases. And this divergence persists when looking at the climate change scenarios. I personally think that it is not surprising given their inaccurate representation of deep water formation in the North Atlantic (see e.g. my publication [22]), but I am biased.

Download the full-text here.

de Boer et al. (2022) The impact of Southern Ocean topographic barriers on the ocean circulation and the overlying atmosphere

A.M. de Boer, D.K. Hutchinson, F. Roquet, L.C. Sime, N.J. Burls, and C. Heuzé (2022) The impact of Southern Ocean topographic barriers on the ocean circulation and the overlying atmosphere, Journal of Climate, vol 35, pp 5805–5821, doi:10.1175/JCLI-D-21-0896.1

Does the seafloor matter for the climate? More specifically, if the under-water mountains were gone, would any climate process be affected? We conducted four model experiments where we flattened a part of the seafloor around the Southern Ocean to answer that question.

The entire climate system was impacted, from the formation of deep water to precipitation. Which in hindsight is not surprising: like mountains on land, these under-water mountains block the flow and force it to go around, taking a longer, different route. If you remove the mountains, the flow can now take the shortest route from A to B. In the Southern Ocean, that meant that the entire water column was modified, fronts were relocated, modifying the temperature/pressure gradients at the ocean surface and lower atmosphere, hence even changing precipitation patterns.

That is: another proof that the deep ocean matters 🙂

The modified Southern Ocean bathymetry: in the red boxes, the usual underwater mountains have been replaced with a flat, deep seafloor. Adapted from Fig. 1b of de Boer et al. (2022)

Download the full-text here.

Mohrmann et al. (2022) Observed Mixing at the Flanks of Maud Rise in the Weddell Sea

M. Mohrmann, S. Swart, and C. Heuzé (2022) Observed Mixing at the Flanks of Maud Rise in the Weddell Sea, Geophysical Research Letters, vol 49, e2022GL098036, doi:10.1029/2022GL098036

At the beginning of his PhD under our supervision, Martin Mohrmann deployed two high frequency autonomous profilers with under ice capability by Maud Rise. That means that even in the middle of winter, we have daily profiles of the water column. The “fun” thing is that they drifted in opposite directions, so their synchronous sampling of two different locations revealed crucial spatial effects in that region.

Key findings (copied from the paper):

  • High frequency (1–3 days) float profiles were collected over both Maud Rise and its vicinity over several seasonal cycles
  • Temperature and salinity below the mixed layer are strongly bathymetry-dependent at Maud Rise
  • Enhanced spiciness variability indicates intrusions and mixing between Maud Rise Deep Water and the surrounding Warm Deep Water

Stay tuned for paper number 3, to be submitted soon, where these profilers are compared to older floats to this time determine the temporal effects.

Download the full text here.

Snoeijs-Lejonmalm et al. (2022) Unexpected fish and squid in the central Arctic deep scattering layer

P. Snoeijs-Leijonmalm, H. Flores, S. Sakinan, N. Hildebrandt, A. Svenson, G. Castellani, K. Vane, F.C. Mark, C. Heuzé, S. Tippenhauer, B. Niehoff, J. Hjelm, J. Hentati Sundberg, F.L. Schaafsma, R. Engelmann and The EFICA-MOSAiC Team (2022) Unexpected fish and squid in the central Arctic deep scattering layer, Science Advances, vol 8, doi:10.1126/sciadv.abj7536

During the MOSAiC expedition, as the ship was embedded in the sea ice pack, one of the ways through which biodiversity and abundance were measured was via the (hydroacoustic) backscatter of the “deep scattering layer”. We find here that the backscatter is strongly correlated to the water mass properties: life, and there’s quite a lot of it, sits primarily in the comparatively warm Atlantic layer.

The team also collected fish samples and recorded hours of video footages. These reveal that, unexpectedly, that layer also contained healthy polar cods and squids.

Extract from Snoeijs-Lejonmalm et al. (2022) Fig. 6: Squid happily swimming around caught on camera

The abundance is way too low for fisheries, but these results prove that the ice-covered Arctic Ocean is far from being the desert it’s often described as (CH’s personal opinion: and consequently, it should be protected accordingly).

Download the full-text here.

Rabe et al. (2022) Overview of the MOSAiC expedition: Physical oceanography

Rabe, B, Heuzé, C, Regnery, J, Aksenov, Y, Allerholt, J, Athanase, M, Bai, Y, Basque, C, Bauch, D, Baumann, TM, Chen, D, Cole, ST, Craw, L, Davies, A, Damm, E, Dethloff, K, Divine, DV, Doglioni, F, Ebert, F, Fang, Y-C, Fer, I, Fong, AA, Gradinger, R, Granskog, MA, Graupner, R, Haas, C, He, H, He, Y, Hoppmann, M, Janout, M, Kadko, D, Kanzow, T, Karam, S, Kawaguchi, Y, Koenig, Z, Kong, B, Krishfield, RA, Krumpen, T, Kuhlmey, D, Kuznetsov, I, Lan, M, Laukert, G, Lei, R, Li, T, Torres-Valdés, S, Lin, L, Lin, L, Liu, H, Liu, N, Loose, B, Ma, X, MacKay, R, Mallet, M, Mallett, RDC, Maslowski, W, Mertens, C, Mohrholz, V, Muilwijk, M, Nicolaus, M, O’Brien, JK, Perovich, D, Ren, J, Rex, M, Ribeiro, N, Rinke, A, Schaffer, J, Schuffenhauer, I, Schulz, K, Shupe, MD, Shaw, W, Sokolov, V, Sommerfeld, A, Spreen, G, Stanton, T, Stephens, M, Su, J, Sukhikh, N, Sundfjord, A, Thomisch, K, Tippenhauer, S, Toole, JM, Vredenborg, M, Walter, M, Wang, H, Wang, L, Wang, Y, Wendisch, M, Zhao, J, Zhou, M, Zhu, J. (2022). Overview of the MOSAiC expedition: Physical oceanography. Elementa: Science of the Anthropocene 10(1). DOI: https://doi.org/10.1525/elementa.2021.00062

In October 2019, the RV Polarstern was purposely frozen in the high Arctic pack ice to be used as a research platform by hundreds of international scientists while the ship drifted along with the ice until September 2020. Or at least, that was the plan of MOSAiC. Covid19 and an extremely rapid transpolar drift made the expedition more… “interesting”. In this overview, we detail the physical oceanography program (of which I was one of the two co-leads for the entire expedition):

  • The measurement systems from the ship, deployed on the ice, and in the distributed network of autonomous sensors up to 50 km around the ship;
  • What we did where and when, including the covid19-related changes of schedules;
  • The “event” measurements: 36h microstucture profiling, sampling in leads, etc.

And we present our first results:

  • The full-depth seasonal and regional variability of the Arctic water masses, including a very visible Atlantification;
  • A way less “quiescent” Arctic than expected, with increased mixing in the upper 500 m consistent with the reduction in sea ice concentration and thickness;
  • Observations of the life cycle of freshwater lenses just under the ice, until their destruction by storms.

This publication is mostly meant as the data paper for all other MOSAiC physical oceanography publications to come, so stay tuned for more actual results.

Download the full-text here.

Shupe et al. (2022) Overview of the MOSAiC expedition—Atmosphere

Shupe, MD, Rex, M, Blomquist, B, Persson, POG, Schmale, J, Uttal, T, Althausen, D, Angot, H, Archer, S, Bariteau, L, Beck, I, Bilberry, J, Bucci, S, Buck, C, Boyer, M, Brasseur, Z, Brooks, IM, Calmer, R, Cassano, J, Castro, V, Chu, D, Costa, D, Cox, CJ, Creamean, J, Crewell, S, Dahlke, S, Damm, E, de Boer, G, Deckelmann, H, Dethloff, K, Dütsch, M, Ebell, K, Ehrlich, A, Ellis, J, Engelmann, R, Fong, AA, Frey, MM, Gallagher, MR, Ganzeveld, L, Gradinger, R, Graeser, J, Greenamyer, V, Griesche, H, Griffiths, S, Hamilton, J, Heinemann, G, Helmig, D, Herber, A, Heuzé, C, Hofer, J, Houchens, T, Howard, D, Inoue, J, Jacobi, H-W, Jaiser, R, Jokinen, T, Jourdan, O, Jozef, G, King, W, Kirchgaessner, A, Klingebiel, M, Krassovski, M, Krumpen, T, Lampert, A, Landing, W, Laurila, T, Lawrence, D, Lonardi, M, Loose, B, Lüpkes, C, Maahn, M, Macke, A, Maslowski, W, Marsay, C, Maturilli, M, Mech, M, Morris, S, Moser, M, Nicolaus, M, Ortega, P, Osborn, J, Pätzold, F, Perovich, DK, Petäjä, T, Pilz, C, Pirazzini, R, Posman, K, Powers, H, Pratt, KA, Preußer, A, Quéléver, L, Radenz, M, Rabe, B, Rinke, A, Sachs, T, Schulz, A, Siebert, H, Silva, T, Solomon, A, Sommerfeld, A, Spreen, G, Stephens, M, Stohl, A, Svensson, G, Uin, J, Viegas, J, Voigt, C, von der Gathen, P, Wehner, B, Welker, JM, Wendisch, M, Werner, M, Xie, ZQ, Yue, F. (2022) Overview of the MOSAiC expedition—Atmosphere. Elementa: Science of the Anthropocene 10(1). DOI: https://doi.org/10.1525/elementa.2021.00060

In October 2019, the RV Polarstern was purposely frozen in the high Arctic pack ice to be used as a research platform by hundreds of international scientists while the ship drifted along with the ice until September 2020. Or at least, that was the plan of MOSAiC. Covid19 and an extremely rapid transpolar drift made the expedition more… “interesting”. In this overview, we detail the atmospheric observation program:

  • The measurement systems from the ship, deployed on the ice, and the crewed and uncrewed flight campaigns;
  • What we did where and when, including the covid19-related changes of schedules;
  • The “event” measurements: radiosonde sampling of warm air intrusion, storms etc.

And present our first results:

  • Record high positive Arctic Oscillation, which contributed to a record ozone hole in the Arctic stratosphere, and to persistent winds that pushed the sea ice and Polarstern more quickly across the Arctic than expected.
  • Dynamic (vertical wind structure and momentum transfer to sea ice and ocean) and thermodynamic (warm air masses) influences of more than 20 Arctic cyclones, or storms, of various scales.
  • Year-round information on variability of atmospheric composition and aerosol populations in the Central Arctic, especially the relative influences of long-range transport versus local processes. 

This publication is mostly meant as the data paper for all other MOSAiC atmosphere publications to come, so stay tuned for more actual results.

Download the full-text here.

Nicolaus et al. (2022) Overview of the MOSAiC expedition: Snow and sea ice

Nicolaus, M, Perovich, DK, Spreen, G, Granskog, MA, Albedyll, LV, Angelopoulos, M, Anhaus, P, Arndt, S, Belter, HJ, Bessonov, V, Birnbaum, G, Brauchle, J, Calmer, R, Cardellach, E, Cheng, B, Clemens-Sewall, D, Dadic, R, Damm, E, de Boer, G, Demir, O, Dethloff, K, Divine, DV, Fong, AA, Fons, S, Frey, MM, Fuchs, N, Gabarró, C, Gerland, S, Goessling, HF, Gradinger, R, Haapala, J, Haas, C, Hamilton, J, Hannula, H-R, Hendricks, S, Herber, A, Heuzé, C, Hoppmann, M, Høyland, KV, Huntemann, M, Hutchings, JK, Hwang, B, Itkin, P, Jacobi, H-W, Jaggi, M, Jutila, A, Kaleschke, L, Katlein, C, Kolabutin, N, Krampe, D, Kristensen, SS, Krumpen, T, Kurtz, N, Lampert, A, Lange, BA, Lei, R, Light, B, Linhardt, F, Liston, GE, Loose, B, Macfarlane, AR, Mahmud, M, Matero, IO, Maus, S, Morgenstern, A, Naderpour, R, Nandan, V, Niubom, A, Oggier, M, Oppelt, N, Pätzold, F, Perron, C, Petrovsky, T, Pirazzini, R, Polashenski, C, Rabe, B, Raphael, IA, Regnery, J, Rex, M, Ricker, R, Riemann-Campe, K, Rinke, A, Rohde, J, Salganik, E, Scharien, RK, Schiller, M, Schneebeli, M, Semmling, M, Shimanchuk, E, Shupe, MD, Smith, MM, Smolyanitsky, V, Sokolov, V, Stanton, T, Stroeve, J, Thielke, L, Timofeeva, A, Tonboe, RT, Tavri, A, Tsamados, M, Wagner, DN, Watkins, D, Webster, M, Wendisch, M. (2022) Overview of the MOSAiC expedition: Snow and sea ice. Elementa: Science of the Anthropocene 10(1). DOI: https://doi.org/10.1525/elementa.2021.000046

In October 2019, the RV Polarstern was purposely frozen in the high Arctic pack ice to be used as a research platform by hundreds of international scientists while the ship drifted along with the ice until September 2020. Or at least, that was the plan of MOSAiC. Covid19 and an extremely rapid transpolar drift made the expedition more… “interesting”. In this overview, we detail the snow and ice observational program:

  • The measurement systems from the ship, deployed on the ice and in the distributed network of autonomous sensors up to 50 km around the ship, and the airborne and satellite observations;
  • What we did where and when, including the covid19-related changes of schedules;
  • The “event” measurements: thin ice formation in leads, rain on snow, etc.

And we present our first results:

  • Larger spatial variabilities of the snow cover than expected, due to atmospheric processes and the structure of the underlying sea ice.
  • More dynamic and faster drifting ice pack than expected. For reference, we covered in 7 months the same distance as Nansen did in 3 years, 1893-1896.
  • Combined remote sensing measurements on the ice with detailed snow and ice observations pave the way for new sea ice observations from upcoming satellite missions and allow better uncertainty assessments of existing satellite time series.

This publication is mostly meant as the data paper for all other MOSAiC snow and ice publications to come, so stay tuned for more actual results.

Download the full-text here.

Zhou et al. (2022) Early winter triggering of the Maud Rise Polynya

L. Zhou, C. Heuzé, and M. Mohrmann (2022) Early winter triggering of the Maud Rise Polynya, Geophysical Research Letters, doi:10.1029/2021GL096246

What triggers the opening of large open-ocean polynyas (holes in the winter pack ice) is still debated as we do not have in-situ observations. The main motivation for our SNSA-funded project “WINDOWS” is to find signatures of upcoming polynya events in widely available remote sensing products, in order for example to re-route autonomous instruments or optimise expeditions.

In a preliminary study [13], we could predict a polynya 5-day ahead of its opening using thermal infrared. In [23], still using thermal infrared, we increased to two weeks. In this study, we use microwave-based retrievals and can predict the opening four months ahead.

We also find that the polynya opens because of both dynamics effects (anomalous wind and ocean currents’ stresses on the sea ice) and thermodynamics, notably anomalous entrainment of heat into the mixed layer.

We’re currently working on

  • estimating energy fluxes and sea ice production in polynyas, both open-ocean and coastal;
  • and improving the sea ice retrievals.

So stay tuned for more polynya results!

Download the full-text here.

Solomon et al. (2021) Freshwater in the Arctic Ocean 2010-2019

A. Solomon, C. Heuzé, B. Rabe, S. Bacon, L. Bertino, P. Heimbach, J. Inoue, D. Iovino, R. Mottram, X. Zhang, Y. Aksenov, R. McAdam, A. Nguyen, R. Raj, and H. Tang (2021) Freshwater in the Arctic Ocean 2010-2019, Ocean Science, vol 17, pp. 1081–1102, doi:10.5194/os-17-1081-2021.

Fig. 2a from Solomon et al. (2021). Freshwater content north of 70N down to the 34 isohaline, for the six ocean reanalyses and the multi model mean (thick red line).

This is a review paper that aimed at determining how the Arctic Ocean freshwater content has changed over the last decade, and why.

Disclaimer: In oceanography, “salt content” is preferable to “freshwater content”, as the latter is based on a somewhat arbitrary choice of reference salinity. However, the vast majority of the published literature still uses freshwater content, as do other fields such as glaciology. Therefore, for this review, we used freshwater content as well.

Our main findings are:

  • Freshwater content increased over 2000-2009 but appears to have stabilised over 2010-2019.
  • This stabilisation is the result of an increase in freshwater content over the Beaufort Gyre and a decrease over the rest of the Arctic.
  • The atmospheric contribution is controlled by the Arctic Oscillation (more moisture transport to the Arctic during a positive phase).
  • The Arctic sea ice has transitioned to a new state: seasonal cover over the shelves, fast transpolar drift. No clear conclusion on the impact of this new sea ice on the ocean and atmosphere in the literature yet.
  • Mass loss from Greenland and other Arctic glaciers has increased.
  • Vertical mixing in the ‘Atlantified’ Arctic has increased and the halocline has weakened.

Our most notable conclusion is that all components of the Arctic climate system, especially rivers, are still unsufficiently monitored to clearly distinguish climate change signal from low frequency variability.

Download the full-text here.

Mohrmann et al. (2021) Southern Ocean polynyas in CMIP6 models

M. Mohrmann, C. Heuzé, and S. Swart (2021) Southern Ocean polynyas in CMIP6 models, The Cryosphere, vol 15, pp. 4281–4313, doi:10.5194/tc-15-4281-2021.

We use daily and monthly sea ice concentration and sea ice thickness output from 27 models that participated in the Climate Model Intercomparison Project phase 6 (CMIP6) to evaluate their representation of polynyas, i.e. openings in the winter sea ice, in the Southern Ocean. We find that:

  • The daily sea ice thickness output has serious issues;
  • Few models have very large open ocean polynyas, but open ocean polynyas feature in most models too often;
  • The majority of models overestimate the area of coastal polynyas;
  • For most models, the polynya occurrence and area is larger if using daily output instead of monthly, or if using sea ice thickness instead of concentration;
  • Too few model families provided CM and ESM versions for us to be certain, but CM versions seem to have a better representation of coastal polynyas, likely because they can be run at higher resolution;
  • The Southern Annular Mode and open ocean polynya activity are surprisingly not correlated in the models. Instead, we find a relationship with the Antarctic Circumpolar Current (ACC): the models with the largest open ocean polynya are the ones with the most realistic ACC, although it is unclear which process causes the other one.
Fig. 4 from Mohrmann et al. (2021) showing the agreement between observations (left) and the highest resolution model (right, 25 km)

Download the full text here.