Lista de obras - Hubertus Fischer - Dominio Público Uruguay

115 year ice-core data from Akademii Nauk ice cap, Severnaya Zemlya: high-resolution record of Eurasian Arctic climate change

scholarly article by Thomas Opel et al published 2009 in Journal of Glaciology

30,000 years of cosmic dust in Antarctic ice.

artículo científico publicado en 2006

9,400 years of cosmic radiation and solar activity from ice cores and tree rings

artículo científico publicado en 2012

A 1,000-year ice core record of interannual to multidecadal variations in atmospheric circulation over the North Atlantic

article published in 2005

A 156 kyr smoothed history of the atmospheric greenhouse gases CO2, CH4, and N2O and their radiative forcing

artículo científico publicado en 2017

A centrifugal ice microtome for measurements of atmospheric CO2 on air trapped in polar ice cores

scholarly article by B. Bereiter et al published 7 February 2013 in Atmospheric Measurement Techniques

A climatological analysis of high-precipitation events in Dronning Maud Land, Antarctica, and associated large-scale atmospheric conditions

article

A gas chromatography/combustion/isotope ratio mass spectrometry system for high-precision delta13C measurements of atmospheric methane extracted from ice core samples

artículo científico publicado en 2008

A gas chromatography/pyrolysis/isotope ratio mass spectrometry system for high-precision deltaD measurements of atmospheric methane extracted from ice cores

artículo científico publicado en 2010

A global picture of the first abrupt climatic event occurring during the last glacial inception

scholarly article

A major glacial-interglacial change in aeolian dust composition inferred from Rare Earth Elements in Antarctic ice

article

A model-based interpretation of low-frequency changes in the carbon cycle during the last 120,000 years and its implications for the reconstruction of atmospheric Δ14C

article

A new Greenland ice core chronology for the last glacial termination

scholarly article by S. O. Rasmussen et al published 2006 in Journal of Geophysical Research

A new method for high-resolution methane measurements on polar ice cores using continuous flow analysis

artículo científico publicado en 2009

A reconstruction of atmospheric carbon dioxide and its stable carbon isotopic composition from the penultimate glacial maximum to the last glacial inception

article

A refined TALDICE-1a age scale from 55 to 112 ka before present for the Talos Dome ice core based on high-resolution methane measurements

A stratigraphic framework for abrupt climatic changes during the Last Glacial period based on three synchronized Greenland ice-core records: refining and extending the INTIMATE event stratigraphy

scholarly article

A sublimation technique for high-precision measurements of δ13CO2 and mixing ratios of CO2 and N2O from air trapped in ice cores

scholarly article by Jochen Schmitt et al published 19 July 2011 in Atmospheric Measurement Techniques

A tephra lattice for Greenland and a reconstruction of volcanic events spanning 25–45 ka b2k

scholarly article by A.J. Bourne et al published June 2015 in Quaternary Science Reviews

Abrupt CO2 release to the atmosphere under glacial and early interglacial climate conditions

artículo científico publicado en 2020

Ammonium and non-sea salt sulfate in the EPICA ice cores as indicator of biological activity in the Southern Ocean

scholarly article

An optimized multi-proxy, multi-site Antarctic ice and gas orbital chronology (AICC2012): 120–800 ka

artículo científico publicado en 2013

Atmospheric decadal variability from high-resolution Dome C ice core records of aerosol constituents beyond the Last Interglacial

article by Matthias Bigler et al published January 2010 in Quaternary Science Reviews

Atmospheric impacts of the strongest known solar particle storm of 775 AD.

artículo científico publicado en 2017

Atmospheric nitrous oxide during the last 140,000years

scholarly article

Atmosphericδ13CO2and its relation topCO2and deep oceanδ13C during the late Pleistocene

Author Correction: Palaeoclimate constraints on the impact of 2 °C anthropogenic warming and beyond

article

Boreal fire records in Northern Hemisphere ice cores: a review

article

CO2 and O2/N2 variations in and just below the bubble–clathrate transformation zone of Antarctic ice cores

scholarly article

Carbon isotope constraints on the deglacial CO₂ rise from ice cores

artículo científico publicado en 2012

Centennial mineral dust variability in high-resolution ice core data from Dome C, Antarctica

scholarly article by Fabrice Lambert published in 2012

Change in dust variability in the Atlantic sector of Antarctica at the end of the last deglaciation

Changes in environment over the last 800,000 years from chemical analysis of the EPICA Dome C ice core

article

Changing boreal methane sources and constant biomass burning during the last termination

artículo científico publicado en 2008

Chemical compositions of solid particles present in the Greenland NEEM ice core over the last 110,000 years

article

Climate of the last million years: new insights from EPICA and other records

scholarly article

Climatic and insolation control on the high-resolution total air content in the NGRIP ice core

Comment on “Synchronous records of pCO2 and Δ14C suggest rapid, ocean-derived pCO2 fluctuations at the onset of Younger Dryas” by Steinthorsdottir et al

scholarly article

Comparative carbon cycle dynamics of the present and last interglacial

article

Connecting the Greenland ice-core and U∕Th timescales via cosmogenic radionuclides: testing the synchroneity of Dansgaard–Oeschger events

scholarly article by Florian Adolphi et al published 20 November 2018 in Climate of the Past

Continuous flow analysis of labile iron in ice-cores

artículo científico publicado en 2013

Corrigendum to Dependence of Eemian Greenland temperature reconstructions on the ice sheet topography" published in Clim. Past, 10, 1221–1238, 2014"

scholarly article by N. Merz et al published 28 August 2014 in Climate of the Past

Corrigendum to High-resolution interpolar difference of atmospheric methane around the Last Glacial Maximum" published in Biogeosciences, 9, 3961–3977, 2012"

scholarly article published in Biogeosciences

Decadal-scale progression of the onset of Dansgaard–Oeschger warming events

article

Dependence of Eemian Greenland temperature reconstructions on the ice sheet topography

scholarly article by N. Merz et al published 25 June 2014 in Climate of the Past

Diffusive equilibration of N2, O2 and CO2 mixing ratios in a 1.5-million-years-old ice core

scientific article published in 2014

Direct linking of Greenland and Antarctic ice cores at the Toba eruption (74 ka BP)

artículo científico publicado en 2013

Dual modes of the carbon cycle since the Last Glacial Maximum

artículo científico publicado en 1999

Earth's radiative imbalance from the Last Glacial Maximum to the present

artículo científico publicado en 2019

Eight glacial cycles from an Antarctic ice core

artículo científico publicado en 2004

Erratum to “Reconstruction of millennial changes in dust emission, transport and regional sea ice coverage using the deep EPICA ice cores from the Atlantic and Indian Ocean sector of Antarctica” [Earth Planet. Sci. Lett. 260 (2007) 340–354]

scholarly article

Estimation and calibration of the water isotope differential diffusion length in ice core records

artículo científico publicado en 2015

Evidence for substantial accumulation rate variability in Antarctica during the Holocene, through synchronization of CO 2 in the Taylor Dome, Dome C and DML ice cores

scholarly article

Evolution of the stable carbon isotope composition of atmospheric CO2over the last glacial cycle

article

Fe2+ in ice cores as a new potential proxy to detect past volcanic eruptions

scientific article published on 07 November 2018

Geochemical and Microbiological Studies of Nitrous Oxide Variations within the New NEEM Greenland Ice Core during the Last Glacial Period

scholarly article by Vanya Miteva et al published 4 September 2015 in Geomicrobiology Journal

Glacial terminations as southern warmings without northern control

article

Glacial/interglacial changes in mineral dust and sea-salt records in polar ice cores: Sources, transport, and deposition

Glacial/interglacial wetland, biomass burning, and geologic methane emissions constrained by dual stable isotopic CH4 ice core records

artículo científico publicado en 2017

Glacial–interglacial and millennial-scale variations in the atmospheric nitrous oxide concentration during the last 800,000 years

scholarly article

Greenland accumulation and its connection to the large-scale atmospheric circulation in ERA-Interim and paleoclimate simulations

scholarly article by N. Merz et al published 4 November 2013 in Climate of the Past

Greenland records of aerosol source and atmospheric lifetime changes from the Eemian to the Holocene.

artículo científico publicado en 2018

High-resolution Greenland ice core data show abrupt climate change happens in few years

artículo científico publicado en 2008

High-resolution aerosol concentration data from the Greenland NorthGRIP and NEEM deep ice cores

artículo científico publicado en 2022

High-resolution carbon dioxide concentration record 650,000-800,000 years before present

artículo científico publicado en 2008

High-resolution interpolar difference of atmospheric methane around the Last Glacial Maximum

artículo científico publicado en 2012

High-resolution isotopic evidence for a potential Saharan provenance of Greenland glacial dust

artículo científico publicado en 2018

High-resolution mineral dust and sea ice proxy records from the Talos Dome ice core

High-resolution record of Northern Hemisphere climate extending into the last interglacial period

artículo científico publicado en 2004

Holocene carbon-cycle dynamics based on CO2 trapped in iceat Taylor Dome, Antarctica

artículo científico publicado en 1999

Holocene climatic changes in Greenland: Different deuterium excess signals at Greenland Ice Core Project (GRIP) and NorthGRIP

scholarly article by Valérie Masson-Delmotte et al published 20 July 2005 in Journal of Geophysical Research

How warm was Greenland during the last interglacial period?

article

Hydrogen isotopes preclude marine hydrate CH4 emissions at the onset of Dansgaard-Oeschger events

artículo científico publicado en 2010

Impact of an abrupt cooling event on interglacial methane emissions in northern peatlands

artículo científico publicado en 2013

Improving accuracy and precision of ice core δD(CH4) analyses using methane pre-pyrolysis and hydrogen post-pyrolysis trapping and subsequent chromatographic separation

scholarly article by Michael Bock et al published 4 July 2014 in Atmospheric Measurement Techniques

In situ observations of the isotopic composition of methane at the Cabauw tall tower site

scholarly article

Independent variations of CH4 emissions and isotopic composition over the past 160,000 years

article

Industrial-era decline in subarctic Atlantic productivity

scientific article published on 06 May 2019

Influence of large-scale teleconnection patterns on methane sulfonate ice core records in Dronning Maud Land

artículo científico publicado en 2006

Is there 1.5 million-year old ice near Dome C, Antarctica?

Is there 1.5-million-year-old ice near Dome C, Antarctica?

artículo científico publicado en 2017

Isotopic constraints on marine and terrestrial N2O emissions during the last deglaciation

artículo científico publicado en 2014

Large-scale spatial trends in recent firn chemistry along an east-west transect through central Greenland

scholarly article by Hubertus Fischer & D. Wagenbach published October 1996 in Atmospheric Environment

Little Ice Age clearly recorded in northern Greenland ice cores

scholarly article by Hubertus Fischer et al published 15 May 1998 in Geophysical Research Letters

Magnitude, frequency and climate forcing of global volcanism during the last glacial period as seen in Greenland and Antarctic ice cores (60–9 ka)

artículo científico publicado en 2022

Millennial changes in North American wildfire and soil activity over the last glacial cycle

article

Millennial-scale atmospheric CO2 variations during the Marine Isotope Stage 6 period (190–135 ka)

artículo científico publicado en 2020

Mode change of millennial CO2 variability during the last glacial cycle associated with a bipolar marine carbon seesaw

artículo científico publicado en 2012

N&lt;sub&gt;2&lt;/sub&gt;O changes from the Last Glacial Maximum to the preindustrial – Part 1: Quantitative reconstruction of terrestrial and marine emissions using N&lt;sub&gt;2&lt;/sub&gt;O stable isotopes in ice c

scientific article published in 2019

N2O changes from the Last Glacial Maximum to the preindustrial – Part 2: terrestrial N2O emissions and carbon–nitrogen cycle interactions

artículo científico publicado en 2020

NGRIP CH4 concentration from 120 to 10 kyr before present and its relation to a δ15N temperature reconstruction from the same ice core

article published in 2014

No support for carbon storage of >1,000 GtC in northern peatlands

On the impact of impurities on the densification of polar firn

On the interference of Kr during carbon isotope analysis of methane using continuous-flow combustion–isotope ratio mass spectrometry

article

Online technique for isotope and mixing ratios of CH4, N2O, Xe and mixing ratios of organic trace gases on a single ice core sample

article

Orbital and millennial Antarctic climate variability over the past 800,000 years.

artículo científico publicado en 2007

Palaeoclimate constraints on the impact of 2 °C anthropogenic warming and beyond ⬇️

article

Prevalence of the Antarctic Circumpolar Wave over the last two millenia recorded in Dronning Maud Land ice

scholarly article

Proxies and measurement techniques for mineral dust in Antarctic ice cores

artículo científico publicado en 2008

Quantitative interpretation of atmospheric carbon records over the last glacial termination

RADIX: a minimal-resources rapid-access drilling system

article published in 2014

Real-time analysis of δ13C- and δD-CH4 in ambient air with laser spectroscopy: method development and first intercomparison results

article

Reconstruction of millennial changes in dust emission, transport and regional sea ice coverage using the deep EPICA ice cores from the Atlantic and Indian Ocean sector of Antarctica

artículo científico publicado en 2007

Representativeness and seasonality of major ion records derived from NEEM firn cores

scholarly article

Retrieving the paleoclimatic signal from the deeper part of the EPICA Dome C ice core

scholarly article

Revision of the EPICA Dome C CO2 record from 800 to 600 kyr before present

scholarly article

Revisiting sites of the South Pole Queen Maud Land Traverses in East Antarctica: Accumulation data from shallow firn cores

article by H. Anschütz et al published 25 December 2009 in Journal of Geophysical Research

Simulating changes in the terrestrial biosphere during the last glacial/interglacial transition

artículo científico publicado en 2004

Simultaneous stable isotope analysis of methane and nitrous oxide on ice core samples

article

Snapshots of mean ocean temperature over the last 700 000 years using noble gases in the EPICA Dome C ice core

artículo científico publicado en 2021

Snow chemistry across Antarctica

scholarly article

Soluble and insoluble lithium dust in the EPICA DomeC ice core—Implications for changes of the East Antarctic dust provenance during the recent glacial–interglacial transition

article published in 2007

Southern Ocean sea-ice extent, productivity and iron flux over the past eight glacial cycles

artículo científico publicado en 2006

Southern Ocean sea-ice extent, productivity and iron flux over the past eight glacial cycles

artículo científico publicado en 2007

Stable carbon cycle-climate relationship during the Late Pleistocene

artículo científico publicado en 2005

Stable isotope constraints on Holocene carbon cycle changes from an Antarctic ice core

artículo científico publicado en 2009

Statistical techniques to select detection thresholds for peak signals in ice-core data

scholarly article

Sulfate and nitrate firn concentrations on the Greenland ice sheet: 2. Temporal anthropogenic deposition changes

scholarly article by Hubertus Fischer et al published 1 September 1998 in Journal of Geophysical Research

Sulfate spikes in the deep layers of EPICA-Dome C ice core: evidence of glaciological artifacts

artículo científico publicado en 2009

Supporting evidence from the EPICA Dronning Maud Land ice core for atmospheric CO2 changes during the past millennium

article

Temperature and mineral dust variability recorded in two low-accumulation Alpine ice cores over the last millennium

The PMIP4 contribution to CMIP6 – Part 2: Two interglacials, scientific objective and experimental design for Holocene and Last Interglacial simulations ⬇️

artículo científico publicado en 2017

The deuterium excess records of EPICA Dome C and Dronning Maud Land ice cores (East Antarctica)

article

The influence of regional circulation patterns on wet and dry mineral dust and sea salt deposition over Greenland

scholarly article by M. A. Hutterli et al published 29 November 2006 in Climate Dynamics

The response of atmospheric nitrous oxide to climate variations during the last glacial period

scholarly article

The role of Southern Ocean processes in orbital and millennial CO2 variations – A synthesis

scholarly article

The role of seasonality of mineral dust concentration and size on glacial/interglacial dust changes in the EPICA Dronning Maud Land ice core

article

Timing and climate forcing of volcanic eruptions for the past 2,500 years.

artículo científico publicado en 2015

Travel and travel reports of German court gardeners in the early nineteenth century, with a focus on Heinrich Ludolph Wendland

journal article; published in Studies in the History of Gardens & Designed Landscapes, Jan 2016

Volcanic climate forcing preceding the inception of the Younger Dryas: Implications for tracing the Laacher See eruption

artículo científico

What caused Earth's temperature variations during the last 800,000 years? Data-based evidence on radiative forcing and constraints on climate sensitivity

artículo científico publicado en 2010

What do accumulation records of single ice cores in Greenland represent?

scholarly article by Traute Crüger et al published 6 November 2004 in Journal of Geophysical Research

Where to find 1.5 million yr old ice for the IPICS "Oldest-Ice" ice core

article by Hubertus Fischer et al published 5 November 2013 in Climate of the Past

Lista de obras de Hubertus Fischer

115 year ice-core data from Akademii Nauk ice cap, Severnaya Zemlya: high-resolution record of Eurasian Arctic climate change

30,000 years of cosmic dust in Antarctic ice.

9,400 years of cosmic radiation and solar activity from ice cores and tree rings

A 1,000-year ice core record of interannual to multidecadal variations in atmospheric circulation over the North Atlantic

A 156 kyr smoothed history of the atmospheric greenhouse gases CO<sub>2</sub>, CH<sub>4</sub>, and N<sub>2</sub>O and their radiative forcing

A centrifugal ice microtome for measurements of atmospheric CO<sub>2</sub> on air trapped in polar ice cores

A climatological analysis of high-precipitation events in Dronning Maud Land, Antarctica, and associated large-scale atmospheric conditions

A gas chromatography/combustion/isotope ratio mass spectrometry system for high-precision delta13C measurements of atmospheric methane extracted from ice core samples

A gas chromatography/pyrolysis/isotope ratio mass spectrometry system for high-precision deltaD measurements of atmospheric methane extracted from ice cores

A global picture of the first abrupt climatic event occurring during the last glacial inception

A major glacial-interglacial change in aeolian dust composition inferred from Rare Earth Elements in Antarctic ice

A model-based interpretation of low-frequency changes in the carbon cycle during the last 120,000 years and its implications for the reconstruction of atmospheric Δ14C

A new Greenland ice core chronology for the last glacial termination

A new method for high-resolution methane measurements on polar ice cores using continuous flow analysis

A reconstruction of atmospheric carbon dioxide and its stable carbon isotopic composition from the penultimate glacial maximum to the last glacial inception

A refined TALDICE-1a age scale from 55 to 112 ka before present for the Talos Dome ice core based on high-resolution methane measurements

A stratigraphic framework for abrupt climatic changes during the Last Glacial period based on three synchronized Greenland ice-core records: refining and extending the INTIMATE event stratigraphy

A sublimation technique for high-precision measurements of δ<sup>13</sup>CO<sub>2</sub> and mixing ratios of CO<sub>2</sub> and N<sub>2</sub>O from air trapped in ice cores

A tephra lattice for Greenland and a reconstruction of volcanic events spanning 25–45 ka b2k

Abrupt CO2 release to the atmosphere under glacial and early interglacial climate conditions

Ammonium and non-sea salt sulfate in the EPICA ice cores as indicator of biological activity in the Southern Ocean

An optimized multi-proxy, multi-site Antarctic ice and gas orbital chronology (AICC2012): 120–800 ka

Atmospheric decadal variability from high-resolution Dome C ice core records of aerosol constituents beyond the Last Interglacial

Atmospheric impacts of the strongest known solar particle storm of 775 AD.

Atmospheric nitrous oxide during the last 140,000years

Atmosphericδ13CO2and its relation topCO2and deep oceanδ13C during the late Pleistocene

Author Correction: Palaeoclimate constraints on the impact of 2 °C anthropogenic warming and beyond

Boreal fire records in Northern Hemisphere ice cores: a review

CO2 and O2/N2 variations in and just below the bubble–clathrate transformation zone of Antarctic ice cores

Carbon isotope constraints on the deglacial CO₂ rise from ice cores

Centennial mineral dust variability in high-resolution ice core data from Dome C, Antarctica

Change in dust variability in the Atlantic sector of Antarctica at the end of the last deglaciation

Changes in environment over the last 800,000 years from chemical analysis of the EPICA Dome C ice core

Changing boreal methane sources and constant biomass burning during the last termination

Chemical compositions of solid particles present in the Greenland NEEM ice core over the last 110,000 years

Climate of the last million years: new insights from EPICA and other records

Climatic and insolation control on the high-resolution total air content in the NGRIP ice core

Comment on “Synchronous records of pCO2 and Δ14C suggest rapid, ocean-derived pCO2 fluctuations at the onset of Younger Dryas” by Steinthorsdottir et al

Comparative carbon cycle dynamics of the present and last interglacial

Connecting the Greenland ice-core and U∕Th timescales via cosmogenic radionuclides: testing the synchroneity of Dansgaard–Oeschger events

Continuous flow analysis of labile iron in ice-cores

Corrigendum to Dependence of Eemian Greenland temperature reconstructions on the ice sheet topography" published in Clim. Past, 10, 1221–1238, 2014"

Corrigendum to High-resolution interpolar difference of atmospheric methane around the Last Glacial Maximum" published in Biogeosciences, 9, 3961–3977, 2012"

Decadal-scale progression of the onset of Dansgaard–Oeschger warming events

Dependence of Eemian Greenland temperature reconstructions on the ice sheet topography

Diffusive equilibration of N<sub>2</sub>, O<sub>2</sub> and CO<sub>2</sub> mixing ratios in a 1.5-million-years-old ice core

Direct linking of Greenland and Antarctic ice cores at the Toba eruption (74 ka BP)

Dual modes of the carbon cycle since the Last Glacial Maximum

Earth's radiative imbalance from the Last Glacial Maximum to the present

Eight glacial cycles from an Antarctic ice core

Erratum to “Reconstruction of millennial changes in dust emission, transport and regional sea ice coverage using the deep EPICA ice cores from the Atlantic and Indian Ocean sector of Antarctica” [Earth Planet. Sci. Lett. 260 (2007) 340–354]

Estimation and calibration of the water isotope differential diffusion length in ice core records

Evidence for substantial accumulation rate variability in Antarctica during the Holocene, through synchronization of CO 2 in the Taylor Dome, Dome C and DML ice cores

Evolution of the stable carbon isotope composition of atmospheric CO2over the last glacial cycle

Fe2+ in ice cores as a new potential proxy to detect past volcanic eruptions

Geochemical and Microbiological Studies of Nitrous Oxide Variations within the New NEEM Greenland Ice Core during the Last Glacial Period

Glacial terminations as southern warmings without northern control

Glacial/interglacial changes in mineral dust and sea-salt records in polar ice cores: Sources, transport, and deposition

Glacial/interglacial wetland, biomass burning, and geologic methane emissions constrained by dual stable isotopic CH4 ice core records

Glacial–interglacial and millennial-scale variations in the atmospheric nitrous oxide concentration during the last 800,000 years

Greenland accumulation and its connection to the large-scale atmospheric circulation in ERA-Interim and paleoclimate simulations

Greenland records of aerosol source and atmospheric lifetime changes from the Eemian to the Holocene.

High-resolution Greenland ice core data show abrupt climate change happens in few years

High-resolution aerosol concentration data from the Greenland NorthGRIP and NEEM deep ice cores

High-resolution carbon dioxide concentration record 650,000-800,000 years before present

High-resolution interpolar difference of atmospheric methane around the Last Glacial Maximum

High-resolution isotopic evidence for a potential Saharan provenance of Greenland glacial dust

High-resolution mineral dust and sea ice proxy records from the Talos Dome ice core

High-resolution record of Northern Hemisphere climate extending into the last interglacial period

Holocene carbon-cycle dynamics based on CO2 trapped in iceat Taylor Dome, Antarctica

Holocene climatic changes in Greenland: Different deuterium excess signals at Greenland Ice Core Project (GRIP) and NorthGRIP

How warm was Greenland during the last interglacial period?

Hydrogen isotopes preclude marine hydrate CH4 emissions at the onset of Dansgaard-Oeschger events

Impact of an abrupt cooling event on interglacial methane emissions in northern peatlands

Improving accuracy and precision of ice core δD(CH<sub>4</sub>) analyses using methane pre-pyrolysis and hydrogen post-pyrolysis trapping and subsequent chromatographic separation

In situ observations of the isotopic composition of methane at the Cabauw tall tower site

Independent variations of CH4 emissions and isotopic composition over the past 160,000 years

Industrial-era decline in subarctic Atlantic productivity

Influence of large-scale teleconnection patterns on methane sulfonate ice core records in Dronning Maud Land

A 156 kyr smoothed history of the atmospheric greenhouse gases CO<sub>2</sub>, CH<sub>4</sub>, and N<sub>2</sub>O and their radiative forcing

N<sub>2</sub>O changes from the Last Glacial Maximum to the preindustrial – Part 1: Quantitative reconstruction of terrestrial and marine emissions using N<sub>2</sub>O stable isotopes in ice c

No support for carbon storage of >1,000 GtC in northern peatlands