Ice Sheet Freshwater Forcing

Table of contents

• Ice Sheet Freshwater Forcing
• Introduction
• Workshop
• Data Products
  • Antarctica
    • Sub-shelf melt
      • Background
      • Data
      • Graphic
    • Iceberg calving
      • Background
      • Data
      • Graphic
    • Iceberg melt locations
      • Background
      • Data
      • Graphic
    • NOTDONE Surface runoff
    • NOTDONE Basal (grounded) runoff
    • Mass change
      • Data
      • Graphic
    • Mass anomaly
      • Data
      • Graphic
  • Greenland
    • Surface runoff
      • Background
      • Data
      • Graphic
    • Discharge
      • Data
      • Graphic
    • Iceberg melt locations
      • Data
      • Graphic
    • Basal runoff
    • Mass anomaly
      • Data
      • Graphic
  • Regions (Name & ID)

Introduction

This repository contains discussions and workbooks (code) from a virtual workshop on Anomalous Freshwater Fluxes.

Included in this repository are:

• GitHub Discussions from before, during, and after the workshop.
• Workbooks (code) used to build data products (e.g. Greenlandic and Antarctic freshwater from surface melt, ice shelf melt, basal melt, icebergs, etc.).
• Examples of data product post-processing to aid modelers who want use the data.

Workshop

The virtual workshop on Anomalous Freshwater Fluxes aimed to capture freshwater fluxes from ice sheets and ice shelves for use in climate models that don’t include interactive ice sheets. The workshop slides, videos, and discussion notes are archived at https://zenodo.org/doi/10.5281/zenodo.11127902.

To stay up-to-date with existing and new discussions, click on the watch button near the top of this page and then select All Activity or Custom > Discussions (and Issues). If you’re new to GitHub, it can be used as a collaborative project management tool (in addition to a code repository). See Braga (2023) http://doi.org/10.1111/2041-210x.14108.

Data Products

There are two types of data products provided here:

1. Freshwater volume flow rate [units: Gt/yr or m^3/s] with a geospatial component of where this freshwater enters the ocean. The geospatial component is a region of interest (ROI) such as `NE` or `SW` for Greenland, or sector number (1 through 18) for Antarctica.
2. Weighted freshwater distribution maps [units: m^-2]. These are maps of where freshwater is distributed within a ROI if not at the coast, for example iceberg melt. These maps are provided in EPSG:4326 (lon,lat) projection.

Filename	Dimensions	Description
AQ_mass_anomaly.nc	region, time	Antarctic mass anomaly (grounded and shelf)
AQ_calving.nc	region, time	Antarctic ice shelf calving
AQ_subshelf_melt.nc	region, time	Antarctic ice shelf basal melting
AQ_grounded_mass_change.nc	region, time	Antarctic grounded mass anomaly
AQ_iceberg_melt.nc	lon, lat	Antarctic iceberg melt by location and magnitude
GL_discharge.nc	region, time	Greenland ice sheet discharge upstream from grounding line
GL_runoff.nc	region, time	Greenland ice sheet and non-ice grounded liquid runoff
GL_mass_anomaly.nc	region, time	Greenland mass anomaly by month and location
GL_iceberg_melt.nc	lon, lat, time	Greenland iceberg melt magnitude by month and location

Antarctica

All products below are split by the Rignot (2017) regions a.k.a. IMBIE 2 regions, with the exception of Antarctic mass change which is only provided for the whole continent.

Sub-shelf melt

Background

• Workbook: ./AQ_subshelf_melt.org

Average of sub-shelf melt estimates from Davison (2023) and Paolo (2024; dataset)

Data

<xarray.Dataset> Size: 9kB
Dimensions:      (time: 31, region: 18)
Coordinates:
  * time         (time) datetime64[ns] 248B 1991-07-01 1992-07-01 ... 2021-07-01
  * region       (region) int32 72B 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
Data variables:
    melt         (region, time) float64 4kB ...
    region_name  (region) int32 72B ...
    baseline     (region) float64 144B ...
    anomaly      (region, time) float64 4kB ...
Attributes:
    description:           Antarctic region sub-shelf melt
    Conventions:           CF-1.8
    date_created:          20250421T155409Z
    title:                 Subshelf melt per region
    history:               See AQ_subshelf_melt.org
    sourc_code_workbook:   See AQ_subshelf_melt.org
    source:                doi:10.5281/ZENODO.8052519
    DOI:                   https://doi.org/10.5281/zenodo.14020895
    original_data_source:  Davison (2023) https://doi.org/10.1126/sciadv.adi0...
    creator_name:          Ken Mankoff
    creator_email:         ken.mankoff@nasa.gov
    institution:           NASA GISS

Graphic

Iceberg calving

Background

• Workbook: ./AQ_calving.org

Antarctic iceberg calving estimates from Davison (2023)

Data

<xarray.Dataset> Size: 12kB
Dimensions:      (region: 18, time: 25)
Coordinates:
  * time         (time) datetime64[ns] 200B 1997-07-01 1998-07-01 ... 2021-07-01
  * region       (region) int32 72B 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
Data variables:
    calving      (region, time) float64 4kB ...
    baseline     (region) float64 144B ...
    anomaly      (region, time) float64 4kB ...
    uncertainty  (region, time) float64 4kB ...
    region_name  (region) <U5 360B ...
Attributes:
    description:           Antarctic region ice shelf calving rate
    Conventions:           CF-1.8
    date_created:          20250421T184648Z
    title:                 Calving per region
    history:               See AQ_calving.org
    sourc_code_workbook:   See AQ_calving.org
    DOI:                   https://doi.org/10.5281/zenodo.14020895
    original_data_source:  Davison (2023) https://doi.org/10.1126/sciadv.adi0...
    creator_name:          Ken Mankoff
    creator_email:         ken.mankoff@nasa.gov
    institution:           NASA GISS

Graphic

Iceberg melt locations

Background

Normalized iceberg melt patterns per region of origin, i.e. for calving in 18 Antarctic-IMBIE2 regions. From a circum-Antarctic 0.25° simulation forced by the recommended normal year of JRA55 repeated 30 years after spin up. The simulation only covers south of 52.25°S, so a part of the melt pattern is missing (11% missing based on Mathiot and Jourdain 2023).

Data

<xarray.Dataset> Size: 226MB
Dimensions:              (region: 18, time: 12, latitude: 360, longitude: 720)
Coordinates:
  * longitude            (longitude) float64 6kB -179.8 -179.2 ... 179.2 179.8
  * latitude             (latitude) float64 3kB -89.75 -89.25 ... 89.25 89.75
  * region               (region) int32 72B 1 2 3 4 5 6 7 ... 13 14 15 16 17 18
  * time                 (time) int8 12B 1 2 3 4 5 6 7 8 9 10 11 12
    spatial_ref          int8 1B ...
Data variables:
    melt                 (region, time, latitude, longitude) float32 224MB ...
    msk_nemo             (latitude, longitude) float32 1MB ...
    region_name          (region) <U5 360B ...
    region_map           (latitude, longitude) int16 518kB ...
    region_map_expanded  (latitude, longitude) int16 518kB ...
Attributes: (12/19)
    description:           Annual JRA55 climatology
    original_data:         NEMO 0.25° simulations by Anna Olive-Abello (in pr...
    script_used:           remap_per_basin.py
    processed_by:          Nicolas Jourdain <nicolas.jourdain@univ-grenoble-a...
    geospatial_lat_min:    -89.75
    geospatial_lat_max:    89.75
    ...                    ...
    source:                doi:10.5281/ZENODO.8052519
    DOI:                   https://doi.org/10.5281/zenodo.14020895
    original_data_source:  Mathiot (2023) https://doi.org/10.5194/os-19-1595-...
    creator_name:          Ken Mankoff
    creator_email:         ken.mankoff@nasa.gov
    institution:           NASA GISS

Graphic

NOTDONE Surface runoff

• Minimal and only on the peninsula. Not done as part of this work.

NOTDONE Basal (grounded) runoff

• Small term (~70 Gt yr^-1 per van Liefferinge (2013), not done as part of this work.

Mass change

• Workbook: ./AQ_grounded.org
• Data product: AQ_grounded_mass_change.nc

Data

<xarray.Dataset> Size: 3kB
Dimensions:      (basins: 18, time: 22)
Coordinates:
  * basins       (basins) int32 72B 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
  * time         (time) datetime64[ns] 176B 2002-07-01 2003-07-01 ... 2023-07-01
Data variables:
    grounded_dm  (basins, time) float64 3kB ...
Attributes: (12/42)
    title:                     Antarctic grounded mass flow rate
    institution:               NASA GISS
    source:                    doi:10.5281/ZENODO.8052519
    history:                   See AQ_grounded.org
    references:                AIS_cci Product User Guide (https://climate.es...
    tracking_id:               e8fca258-8e11-4e80-86a2-fcf9bf5405ff
    ...                        ...
    sensor:                    KBR, ACC, GPS
    spatial_resolution:        data resolution: ~350km, grid resolution: 50x5...
    key_variables:             change_in_land_ice_amount
    source_code_workbook:      AQ_grounded.org
    DOI:                       https://doi.org/10.5281/zenodo.14020895
    original_data_source:      Dohne (2023) https://doi.org/10.1007/s00190-02...

Graphic

Mass anomaly

• Workbook: ./AQ_mass_anomaly.org
• Data product: AQ_mass_anomaly.nc

Data

<xarray.Dataset> Size: 20kB
Dimensions:        (time: 34, region: 18)
Coordinates:
  * time           (time) datetime64[ns] 272B 1990-07-01 ... 2023-07-01
Dimensions without coordinates: region
Data variables:
    calve          (region, time) float64 5kB ...
    subshelf_melt  (region, time) float64 5kB ...
    grounded_loss  (region, time) float64 5kB ...
    MB_ROI_anom    (region, time) float64 5kB ...
Attributes:
    Creator:               Ken Mankoff
    Conventions:           CF-1.8
    date_created:          20250502T211720Z
    title:                 Antarctic freshwater anomaly
    history:               See AQ_mass_anomaly.org
    source_code_workbook:  AQ_mass_anomaly.org
    source:                doi:10.5281/ZENODO.8052519
    DOI:                   https://doi.org/10.5281/zenodo.14020895
    original_data_source:  Davison (2023) https://doi.org/10.1126/sciadv.adi0...
    creator_name:          Ken Mankoff
    creator_email:         ken.mankoff@nasa.gov
    institution:           NASA GISS

Graphic

Greenland

All products below are split by the Mouginot (2019) regions

Surface runoff

Background

This data product is MAR runoff distributed into Mouginot (2019) http://doi.org/10.7280/d1wt11 regions, but processed at stream level by Mankoff (2020) http://doi.org/10.5194/essd-12-2811-2020. The data includes ‘ice runoff’ which comes from melted ice, snow, and rain on the ice sheet, and ‘land runoff’ which comes from melted snow and rain on land. Runoff is routed through individual streams (subglacial for ice, sub-aerial for land). Both ice-sourced and land-sourced runoff can enter the ocean either at the surface (from a terrestrial stream) or at depth subglacially. This value is estimated per stream. When summing subglacial discharge by ROI, the minimum submarine discharge depth is provided for each ROI.

• Workbook: ./GL_runoff.org
• Data product: GL_runoff.nc

Data

<xarray.Dataset> Size: 203kB
Dimensions:                         (region: 7, time: 876)
Coordinates:
  * region                          (region) int32 28B 1 2 3 4 5 6 7
  * time                            (time) datetime64[ns] 7kB 1950-01-01 ... ...
Data variables:
    subglacial_discharge_from_land  (region, time) float64 49kB ...
    surface_runoff_from_land        (region, time) float64 49kB ...
    subglacial_discharge_from_ice   (region, time) float64 49kB ...
    surface_runoff_from_ice         (region, time) float64 49kB ...
    min_discharge_depth             (region) float32 28B ...
    region_name                     (region) <U2 56B ...
Attributes:
    Conventions:           CF-1.8
    date_created:          20250421T155517Z
    title:                 Ice sheet runoff by Mougniot region
    history:               See GL_runoff.org
    source_code_workbook:  GL_runoff.org
    source:                doi:10.5281/ZENODO.8052519
    DOI:                   https://doi.org/10.5281/zenodo.14020895
    original_data_source:  Mankoff (2020) https://doi.org/10.5194/essd-12-281...
    creator_name:          Ken Mankoff
    creator_email:         ken.mankoff@nasa.gov
    institution:           NASA GISS

Graphic

Discharge

This product is generated from flux gates ~5 km upstream of the terminus.

It lacks:

• Terminus retreat, which should add ~10 % over the last two decades
• Splitting output between icebergs and submarine melt, which is ~50 % +- 30 % (Rignot 2010)
• Peripheral glaciers which is ~5 Gt/yr at present (see Bollen 2013)
• Workbook: ./GL_discharge.org
• Data product: GL_discharge.nc

Data

<xarray.Dataset> Size: 17kB
Dimensions:      (region: 7, time: 186)
Coordinates:
  * time         (time) datetime64[ns] 1kB 1840-01-01 1841-01-01 ... 2025-01-01
  * region       (region) int64 56B 1 2 3 4 5 6 7
Data variables:
    discharge    (region, time) float64 10kB ...
    err          (region, time) float32 5kB ...
    region_name  (region) <U2 56B ...
Attributes: (12/17)
    featureType:           timeSeries
    title:                 Greenland ice sheet discharge by Mouginot region
    summary:               Greenland ice sheet mass balance from 1840 through...
    keywords:              Greenland; Mass; Mass balance
    source:                doi:10.5281/ZENODO.8052519
    creator_name:          Ken Mankoff
    ...                    ...
    Conventions:           CF-1.8
    date_created:          20250421T155603Z
    history:               See GL_discharge.org
    source_code_workbook:  GL_discharge.org
    DOI:                   https://doi.org/10.5281/zenodo.14020895
    original_data_source:  Mankoff (2020) https://doi.org/10.5194/essd-12-136...

Graphic

Iceberg melt locations

This dataset provides spatial maps of iceberg meltwater based on iceberg source. Maps are weighted masks where each region sums to one, plus one all-Greenland weighted map.

• Workbook: ./GL_iceberg_melt.org
• Data product: GL_iceberg_melt.nc

Data

<xarray.Dataset> Size: 177MB
Dimensions:              (region: 7, time: 12, longitude: 720, latitude: 360)
Coordinates:
  * region               (region) int8 7B 1 2 3 4 5 6 7
  * time                 (time) int8 12B 1 2 3 4 5 6 7 8 9 10 11 12
  * longitude            (longitude) float64 6kB -179.8 -179.2 ... 179.2 179.8
  * latitude             (latitude) float64 3kB -89.75 -89.25 ... 89.25 89.75
Data variables:
    melt                 (region, time, latitude, longitude) float64 174MB ...
    melt_GL              (latitude, longitude) float64 2MB ...
    region_map           (latitude, longitude) int8 259kB ...
    region_map_expanded  (latitude, longitude) int8 259kB ...
    region_name          (region) <U2 56B ...
    spatial_ref          int8 1B ...
Attributes: (12/15)
    geospatial_lat_min:    -90
    geospatial_lat_max:    90
    geospatial_lon_min:    -180
    geospatial_lon_max:    180
    Conventions:           CF-1.8
    date_created:          20250421T160954Z
    ...                    ...
    source:                doi:10.5281/ZENODO.8052519
    DOI:                   https://doi.org/10.5281/zenodo.14020895
    original_data_source:  Marson (2024) https://doi.org/10.1029/2023jc020697 
    creator_name:          Ken Mankoff
    creator_email:         ken.mankoff@nasa.gov
    institution:           NASA GISS

Graphic

Basal runoff

This product splits basal melt from Karlsson (2021) http://doi.org/10.1038/s41467-021-23739-z into regions, with two products per region: Water that enters fjords at their surface from sub-aerial streams, and water that enters subglacially.

• Workbook: ./GL_basal_melt.org
• Data product: GL_basal_melt.nc

Mass anomaly

This product uses the discharge product and has all of those limitations.

• Workbook: ./GL_mass_anomaly.org
• Data product: GL_mass_anomaly.nc

Data

<xarray.Dataset> Size: 57kB
Dimensions:       (region: 7, time: 175)
Coordinates:
  * time          (time) datetime64[ns] 1kB 1850-01-01 1851-01-01 ... 2024-01-01
  * region        (region) int32 28B 1 2 3 4 5 6 7
Data variables:
    SMB_ROI       (region, time) float32 5kB ...
    SMB_ROI_err   (region, time) float32 5kB ...
    D_ROI         (region, time) float32 5kB ...
    D_ROI_err     (region, time) float32 5kB ...
    region_name   (region) <U2 56B ...
    MB_ROI        (region, time) float64 10kB ...
    MB            (time) float64 1kB ...
    D_ROI_anom    (region, time) float64 10kB ...
    SMB_ROI_anom  (region, time) float32 5kB ...
    MB_ROI_anom   (region, time) float64 10kB ...
Attributes: (12/17)
    featureType:           timeSeries
    title:                 Greenland ice sheet mass balance by Mouginot region
    summary:               Greenland ice sheet mass balance from 1840 through...
    keywords:              Greenland; Mass; Mass balance
    source:                doi:10.5281/ZENODO.8052519
    creator_name:          Ken Mankoff
    ...                    ...
    Conventions:           CF-1.8
    date_created:          20250502T203459Z
    history:               See GL_mass_anomaly.org
    source_code_workbook:  GL_mass_anomaly.org
    DOI:                   https://doi.org/10.5281/zenodo.14020895
    original_data_source:  Mankoff (2021) https://doi.org/10.5194/essd-13-500...

Graphic

Regions (Name & ID)