Ocean and Cryosphere in Climate

Topic 2 will advance the understanding of past, present and future changes of the climate system from an ocean and cryosphere perspective by closing critical knowledge gaps related to warming climates, variability and extremes as well as sea level change for the benefit of society.

The atmospheric concentrations of carbon dioxide and methane, which are currently by far the highest for at least 800,000 years as a result of anthropogenic influence, is strongly affecting the ocean and cryosphere. We focus on natural and anthropogenically-induced variability as well as on feedbacks in the coupled Earth system via observations, data analyses and comprehensive modeling. Essential are furthermore reconstructions of the past which bring our current changes into the long-term perspective.

An overview by Topic speaker Gerrit Lohmann

Structure

Warming climates

A key objective of this Subtopic is to achieve an improved understanding of the causes and consequences of the 20th- and early 21st-century global and regional anthropogenically-induced warming and its interplay with the natural variability of the climate system from an ocean and cryosphere perspective, and to turn this knowledge into improved climate change projections, in particular in the polar regions. The dedicated investigation of past warming climates will provide unique ways of evaluating the sensitivity of the Earth system under variable boundary conditions and to define its tipping points and deviations from the mean state beyond the presently prevailing range of climates documented by the instrumental record. We will release comprehensive data sets of key climate variables including challenging autonomous and remote sensing-based winter observations from remote polar regions (MOSAiC) and will ensure the transfer of the new knowledge to policymakers and society at large.

Speakers: Martin Frank (GEOMAR) and Gesine Mollenhauer (AWI)

Variability and extremes

Subtopic 2.2 will unravel the structure and dynamics of natural decadal-to-centennial climate variability and improve its simulation in climate models. It will determine possible links between relatively slow natural climate variability and rapid climate extremes, and characterize and quantify extreme events in a changing climate on regional scales (e.g., heatwaves in Europe, sea ice minima in the Arctic and super El Niños in the tropics). Special attention will be paid to teleconnections between the tropics, polar regions and mid-latitudes. Finally, ST2.2 will determine environmental predictability on daily to decadal time scales and contribute to advanced forecasting capabilities

Speakers: Thomas Laepple (AWI) and Peter Brandt (GEOMAR)

Sea level change

We aim to develop and implement sustained monitoring and reconstruction capacities of both sources and regional distributions of sea level change. The combination of present-day observations and process modeling with reconstructions based on proxy-based records of past sea level changes associated with ice sheet collapses will allow us to gain critical understanding of processes that are currently not well represented in Earth system models. Furthermore, we intend to quantify global and regional sea level changes. By combining complementary monitoring systems as well as forward and data-constrained modeling approaches, we will separate and quantify individual processes, in particular, changes in ocean mass and heat content, continental discharge and ice mass balances, and deformation-induced changes in basin geometry. These activities will guide the development of an advanced Earth system model that is capable of simulating sea level changes with unprecedented trustworthiness. We also aim to provide regional projections of sea level change with well-defined uncertainties arising from both, climate scenarios and sources of sea level change. Through collaboration with coastal modelers in T4, information about coastal sea level change will be provided.

Speakers: Henryk Dobslaw (GFZ) and Torsten Kanzow (AWI)

Advanced research methodologies for tomorrow

The main objective of this Subtopic is to improve the methodological basis of research carried out in T2 and beyond. This will be achieved through the development of new observational techniques (e.g., modular observing systems, such as MOSES, FRAM, ARCHES and SMART cables; upgrade of robotic technologies by joint investments as proposed in MUSE), space geodetic observations (e.g., proposed next-generation MCM, innovative GNSS applications, contributions to the SLR and VLBI Global Observing Systems), paleo proxies (e.g., advanced proxy calibrations, chronologies, synchronization of archives) and novel modeling capacities (e.g., global modeling with regionally refined resolution and data assimilation techniques), including models that capture a wide range of resolutions and processes (e.g., tides, surface waves). The rapidly evolving field of data science will also be exploited (e.g., efficient analysis of big data, machine learning, visual analytics).

Speakers: Ilka Weikusat (AWI) and Frank Flechtner (GFZ)

Recent Highlights

Evolution of the most powerful ocean current on Earth

Ocean sediment cores reveal climate-related fluctuations in the Antarctic Circumpolar Current in past epochs

The Antarctic Circumpolar Current plays an important part in global overturning circulation, the exchange of heat and CO2 between the ocean and atmosphere, and the stability of Antarctica’s ice sheets. An international research team led by the Alfred Wegener Institute and the Lamont-Doherty Earth Observatory have now used sediments taken from the South Pacific to reconstruct the flow speed in the last 5.3 million years. Their data show that during glacial periods, the current slowed; during interglacials, it accelerated. Consequently, if the current global warming intensifies in the future, it could mean that the Southern Ocean stores less CO2 and that more heat reaches Antarctica.