The sea ice export out of the Arctic Ocean through Fram Strait into the Greenland Sea is the single largest source of freshwater in the Nordic Seas and therefore of spezial importance for the hydrological cycle of the North Atlantic. On its way south, the exported sea ice melts and thereby modifies the stratification of the ocean surface mixed layer, which in turn influences oceanic deep convection and water mass transformation processes in the Nordic Seas and thus impact global ocean thermohaline circulation. The lack of spatial sea ice thickness information has been one of the weaknesses for previous existing methods to determine the sea ice export. In this study a new method to obtain the sea ice volume flux exclusively from satellite measurements is presented. Previous estimates of the sea ice volume flux relayed on ice draft measurements of a single Upward Looking Sonar (ULS) in the Greenland Sea. The GLAS laser altimeter onboard the ICESat satellite launched in 2003 offers for the first time the opportunity to obtain the spatial sea ice thickness distribution up to 86°N latitude. In this study a method to determine the sea ice freeboard from ICESat altimeter data is developed and applied to nine ICESat measurement periods between 2003 and 2007. Assuming hydrostatic balance and by utilization of further satellite, in situ and climatological data these sea ice freeboard measurements are converted to sea ice thickness maps of the Fram Strait region. The satellite-based ice thickness estimates are combined with sea ice area and sea ice drift, as retrieved from AMSR-E microwave radiometer measurements at 89GHz, to obtain the sea ice volume flux. The errors of the input quantities and the final sea ice volume flux are assessed. Using this method the spatial sea ice volume flux distribution is obtained from satellite observations for the first time. The Fram Strait sea ice volume flux is further investigated by calculating a monthly sea ice volume flux time series between January 2003 and April 2007. Summer months have to be disregarded due to missing sea ice drift data. The sea ice volume flux shows large interannual and -seasonal variability. A mean monthly Fram Strait sea ice volume flux of (248±90) km3/month with respective minimum and maximum values of 112 km3/month (May 2003) and 484 km3/month (December 2004) was found...
Table of Contents
1 Introduction
1.1 Aims
1.2 Structure
1.3 Publications
2 Fundamentals: The Arctic Climate System, Instruments and Data
2.1 The Arctic Climate System
2.1.1 The Arctic
2.1.2 The Arctic Ocean
2.1.3 Sea Ice
2.2 Instruments and Data
2.2.1 ICESat/GLAS
2.2.2 AMSR-E
2.2.3 QuikSCAT/SeaWinds
2.2.4 SAR Data
2.2.5 Polar Stereographic Projection and Study Region
3 Sea Ice Concentration
3.1 Introduction
3.2 ARTIST Sea Ice (ASI) Algorithm
3.2.1 Weather Filters
3.2.2 ASI Results
3.3 Tie-point Sensitivity Analysis
3.4 Error Estimation
3.5 Comparison to Ship Based Observations
3.6 AMSR-E Ice Concentration Algorithm Intercomparison
3.7 2007 Arctic Sea Ice Minimum and AMSR-E Time Series
3.8 Sea Ice Concentration Discussion
3.9 Sea Ice Concentration Summary
4 Sea Ice Drift
4.1 IFREMER AMSR-E 89 GHz Sea Ice Drift Product
4.2 SAR Sea Ice Drift and Comparison to Buoy Ice Drift
4.3 Validation of AMSR-E Ice Drift with SAR Ice Drift Data
4.4 Sea Ice Drift Summary
5 Sea Ice Thickness
5.1 Sea Ice Freeboard
5.1.1 Geoid
5.1.2 Lowest-Level Elevation Method
5.1.3 Validation
5.1.4 Gridded Freeboard
5.1.5 Outlook: Freeboard
5.2 Conversion of Freeboard to Ice Thickness
5.2.1 QuikSCAT Multi-Year Sea Ice Concentration
5.2.2 Snow Thickness and Density
5.2.3 Sea Ice Thickness Maps 2003–2007
5.2.4 Comparison to Ice Thickness From Helicopter-Borne EM-Sounding
5.3 Sea Ice Thickness Conclusion
6 Sea Ice Volume Flux: Determination and Physical Interpretation
6.1 Sea Ice Volume Flux Calculation
6.2 Sea Ice Volume Flux Discussion
6.3 Divergence of Sea Ice Volume Flux
6.4 Fram Strait Sea Ice Volume Flux
6.4.1 Fram Strait Sea Ice Volume Flux for ICESat periods 2003–2007
6.4.2 Monthly Fram Strait Sea Ice Volume Flux Time Series 2003–2007
6.5 Error Evaluation and Comparison to Alternative Methods
6.5.1 Comparison to Volume Flux Obtained Using QuikSCAT Ice Drift
6.5.2 Sensitivity Study
6.5.3 Volume Flux from ULS and ICESat Ice Thickness Measurements
6.6 Comparison to Model Data
6.7 Comparison to Oceanographic Measurements
7 Conclusion
7.1 Summary
7.2 Relevance
7.3 Outlook
A Appendix
A.1 Unusable and Missing Data
A.2 Freeboard – SAR Comparison
A.3 Additionally Used ICESat Ice Thickness Data
A.4 Ice Volume Flux Through Transects
A.5 1990–2007 Fram Strait Sea Ice Volume Flux Data
A.6 NAOSIM and MIT Ice Volume Flux
Objectives and Research Themes
The primary objective of this dissertation is to establish an exclusively satellite-based methodology for monitoring sea ice volume flux in the Fram Strait region, addressing the lack of high-resolution spatial coverage in traditional measurement techniques.
- Development of a combined multi-sensor satellite approach to derive ice volume flux.
- Calculation and analysis of a multi-year monthly time series of sea ice volume flux through the Fram Strait.
- Validation of satellite-derived datasets (concentration, drift, thickness) against in situ and alternative observational data.
- Comparative analysis of satellite-based findings with oceanographic salinity measurements and coupled ice-ocean models.
Excerpt from the Book
1 Introduction
Arctic sea ice: Where does it come from? Where does it go? The most fundamental answers to these questions were already given by Fridtjof Nansen in 1896. His vessel Fram, which entered the Arctic pack ice in the Laptev Sea near the New Siberian Islands in 1893, left the ice again in August 1896 in the Fram Strait after three years of ice drift (Nansen, 1897). Since then we know that the main transport of sea ice out of the Arctic Ocean is taking place via Fram Strait and that the source regions for this ice are as far away as the East Siberian Sea on the opposite side of the Arctic Ocean. Nansen also anticipated the importance of sea ice for the Earth’s climate system when he described sea ice ocean interactions (Nansen, 1902). However, an accurate knowledge of sea ice dynamics and “where the ice goes” still remains an open question and is also the main topic of this work. Sea ice was realized to be one of the key components of the climate system and its interaction with the ocean and atmosphere has not only local but global relevance (ACIA, 2004, 2005). Thus here the variability of the Arctic sea ice mass exchange with the Greenland Sea and the possibilities of regularly monitoring it are in the focus.
In this study a technique to derive the sea ice volume transported out of the Arctic Ocean through Fram Strait entirely from satellite measurements is described. It is a multi-sensor study, where different data products from different satellites are combined. For the observation of the sea ice thickness a new method was developed. This is of special importance as before sea ice thickness could only be measured by in situ campaigns and moorings. Finally a time series of the ice volume transport from Fram Strait for 2003 to 2007 is presented. Monitoring anomalies in the Fram Strait sea ice volume flux is of special importance, as they can influence watermass transformation processes in the Greenland Sea and further downstream in the Atlantic Ocean.
Summary of Chapters
1 Introduction: Provides an overview of the significance of sea ice transport in the Arctic and outlines the research aims and structure of the thesis.
2 Fundamentals: The Arctic Climate System, Instruments and Data: Introduces the Arctic climate system, sea ice properties, and the specific satellite instruments utilized throughout the study.
3 Sea Ice Concentration: Describes the ASI algorithm for determining sea ice concentration from AMSR-E data, including weather filtering and performance validation.
4 Sea Ice Drift: Details the calculation of sea ice drift using AMSR-E data and validates the product against SAR imagery and buoy observations.
5 Sea Ice Thickness: Explains the development of a new method to derive sea ice freeboard from ICESat data and its conversion into ice thickness.
6 Sea Ice Volume Flux: Determination and Physical Interpretation: Presents the final derivation of sea ice volume flux and interprets the results in relation to climate models and oceanographic measurements.
7 Conclusion: Summarizes the study’s achievements, discusses the relevance of the findings, and suggests future research directions.
Keywords
Sea ice, Arctic Ocean, Fram Strait, satellite remote sensing, ICESat, AMSR-E, sea ice volume flux, sea ice concentration, sea ice drift, sea ice thickness, climate system, oceanic circulation, remote sensing validation, hydrology.
Frequently Asked Questions
What is the primary focus of this research?
The research focuses on quantifying the transport of sea ice out of the Arctic Ocean through the Fram Strait using exclusively satellite-based remote sensing data.
What are the central thematic areas?
The study centers on sea ice concentration, ice drift, and sea ice thickness, which are the fundamental parameters required to estimate volume flux.
What is the core objective of the work?
The primary goal is to develop and validate a satellite-based method to continuously monitor sea ice volume flux, addressing historical data gaps that previously necessitated in-situ measurements.
Which scientific methods are applied?
The study employs a multi-sensor approach, utilizing data from satellites like ICESat (for thickness/freeboard) and AMSR-E (for concentration and drift), combined with mathematical algorithms for data processing, interpolation, and uncertainty quantification.
What does the main body of the work cover?
The chapters detail the fundamental characteristics of the Arctic climate system, the specific technical algorithms used for each data product (concentration, drift, thickness), and the final synthesis of these parameters to determine ice volume flux.
Which keywords define this research?
Key terms include sea ice, Arctic Ocean, Fram Strait, satellite remote sensing, ICESat, AMSR-E, and ice volume flux.
How does the author handle data gaps in the time series?
The author uses interpolative methods, such as kriging and the integration of seasonal cycles derived from ULS (Upward Looking Sonar) data, to estimate ice thickness and flux during periods where direct satellite data coverage is sparse.
Why is the Fram Strait region particularly significant?
The Fram Strait is the primary outflow pathway for Arctic sea ice into the North Atlantic, making it a critical control point for freshwater export and a driver for deep-water formation and global thermohaline circulation.
- Quote paper
- Dr. Gunnar Spreen (Author), 2008, Satellite-based Estimates of Sea Ice Volume Flux: Applications to the Fram Strait Region, Munich, GRIN Verlag, https://www.grin.com/document/113252
