diff --git a/configs/common/packages.yaml b/configs/common/packages.yaml
index 72e0356a8..9bae2c5c1 100644
--- a/configs/common/packages.yaml
+++ b/configs/common/packages.yaml
@@ -76,6 +76,10 @@ packages:
     #  message: "Extra ESMF compile options for GCC"
     prefer:
     - '+python'
+  # To avoid duplicate packages (concretizer bug?)
+  expat:
+    require:
+    - '~libbsd'
   fckit:
     require: '@0.13.2 +eckit'
   fftw:
diff --git a/configs/sites/tier1/atlantis/compilers.yaml b/configs/sites/tier1/atlantis/compilers.yaml
index c7c48def4..c2250ac45 100644
--- a/configs/sites/tier1/atlantis/compilers.yaml
+++ b/configs/sites/tier1/atlantis/compilers.yaml
@@ -16,7 +16,7 @@ compilers:
       prepend_path:
         PATH: /cm/local/apps/gcc/11.2.0/bin
         CPATH: /cm/local/apps/gcc/11.2.0/include
-        LD_LIBRARY_PATH: /cm/shared/apps/slurm/21.08.8/lib64:/cm/shared/apps/intel/oneapi/compiler/2022.1.0/linux/compiler/lib/intel64_lin
+        LD_LIBRARY_PATH: /cm/shared/apps/intel/oneapi/compiler/2022.1.0/linux/compiler/lib/intel64_lin:/cm/local/apps/gcc/11.2.0/lib64:/cm/local/apps/gcc/11.2.0/lib
     extra_rpaths: []
 - compiler:
     spec: gcc@11.2.0
@@ -44,15 +44,14 @@ compilers:
     target: x86_64
     modules:
     - intel-oneapi-2024.2.1
+    - tbb/2021.13
     - compiler-rt/2024.2.1
     - compiler/2024.2.1
     environment:
       prepend_path:
         PATH: /cm/local/apps/gcc/11.2.0/bin
         CPATH: /cm/local/apps/gcc/11.2.0/include
-        LD_LIBRARY_PATH: /cm/shared/apps/slurm/21.08.8/lib64:/cm/shared/apps/slurm/21.08.8/lib64/slurm:/cm/shared/apps/intel/oneapi-2024.2.1/compiler/2024
-      append_path:
-        CPATH: /cm/shared/apps/intel/oneapi-2024.2.1/compiler/2024.2/opt/compiler/include/intel64/
+        LD_LIBRARY_PATH: /cm/local/apps/gcc/11.2.0/lib64:/cm/local/apps/gcc/11.2.0/lib
     extra_rpaths: []
 #- compiler:
 #    spec: oneapi@2025.0.3
@@ -73,7 +72,5 @@ compilers:
 #      prepend_path:
 #        PATH: /cm/local/apps/gcc/11.2.0/bin
 #        CPATH: /cm/local/apps/gcc/11.2.0/include
-#        LD_LIBRARY_PATH: /cm/shared/apps/slurm/21.08.8/lib64:/cm/shared/apps/slurm/21.08.8/lib64/slurm:/gpfs/neptune/spack-stack/oneapi-2025.0.3/compiler/2025.0
-#      append_path:
-#        CPATH: /gpfs/neptune/spack-stack/oneapi-2025.0.3/compiler/2025.0/opt/compiler/include/intel64
+#        LD_LIBRARY_PATH: /cm/local/apps/gcc/11.2.0/lib64:/cm/local/apps/gcc/11.2.0/lib
 #    extra_rpaths: []
diff --git a/configs/sites/tier1/atlantis/packages_gcc.yaml b/configs/sites/tier1/atlantis/packages_gcc.yaml
index bc10f8b75..0d85ceef2 100644
--- a/configs/sites/tier1/atlantis/packages_gcc.yaml
+++ b/configs/sites/tier1/atlantis/packages_gcc.yaml
@@ -11,3 +11,4 @@ packages:
     - spec: openmpi@4.1.5%gcc@=11.2.0~cuda~cxx~cxx_exceptions~java~memchecker+pmi~static~wrapper-rpath fabrics=ucx schedulers=slurm
       modules:
       - openmpi/mlnx/gcc/64/4.1.5a1
+      - slurm
diff --git a/configs/sites/tier1/nautilus/compilers.yaml b/configs/sites/tier1/nautilus/compilers.yaml
index 147614a13..05a504822 100644
--- a/configs/sites/tier1/nautilus/compilers.yaml
+++ b/configs/sites/tier1/nautilus/compilers.yaml
@@ -84,22 +84,6 @@ compilers:
 #      append_path:
 #        CPATH: '/p/app/projects/NEPTUNE/spack-stack/oneapi-2025.0.0/compiler/2025.0/opt/compiler/include/intel64'
 #    extra_rpaths: []
-- compiler:
-    spec: gcc@12.2.1
-    paths:
-      cc: /opt/rh/gcc-toolset-12/root/usr/bin/gcc
-      cxx: /opt/rh/gcc-toolset-12/root/usr/bin/g++
-      f77: /opt/rh/gcc-toolset-12/root/usr/bin/gfortran
-      fc: /opt/rh/gcc-toolset-12/root/usr/bin/gfortran
-    flags: {}
-    operating_system: rhel8
-    target: x86_64
-    modules:
-    - slurm
-    - scl/gcc-toolset-12
-    environment: {}
-    extra_rpaths: []
-# Required for Intel backend
 - compiler:
     spec: gcc@11.2.1
     paths:
diff --git a/configs/sites/tier1/nautilus/packages_gcc.yaml b/configs/sites/tier1/nautilus/packages_gcc.yaml
index 2e47c9e0e..1f6fd7a54 100644
--- a/configs/sites/tier1/nautilus/packages_gcc.yaml
+++ b/configs/sites/tier1/nautilus/packages_gcc.yaml
@@ -1,34 +1,14 @@
 packages:
-# On Nautilus, use intel-oneapi-mkl as provider
-# for blas, lapack, fftw-api with GNU because of
-# problems using openblas in downstream applications
-# (e.g. py-pandas):
-# ELF load command address/offset not properly aligned" when loading libopenblas.so
-# https://github.com/OpenMathLib/OpenBLAS/wiki/Faq#ELFoffset
   all:
-    compiler:: [gcc@12.2.1]
+    compiler:: [gcc@11.2.1]
     providers:
       mpi:: [openmpi@5.0.1]
-      blas:: [intel-oneapi-mkl]
-      fftw-api:: [intel-oneapi-mkl]
-      lapack:: [intel-oneapi-mkl]
   mpi:
     buildable: False
   openmpi:
     externals:
-    - spec: openmpi@5.0.1%gcc@12.2.1~cuda~java~memchecker~static~wrapper-rpath fabrics=ucx schedulers=slurm
+    - spec: openmpi@5.0.1%gcc@11.2.1~cuda~java~memchecker~static~wrapper-rpath fabrics=ucx schedulers=slurm
       prefix: /p/app/penguin/openmpi/5.0.1/gcc-8.5.0
       modules:
       - penguin/openmpi/5.0.1/gcc-8.5.0
       - slurm
-  openblas:
-    buildable: False
-  ectrans:
-    require::
-    - '@1.2.0 +mkl ~fftw'
-  gsibec:
-    require::
-    - '@1.2.1 +mkl'
-  py-numpy:
-    require::
-    - '^intel-oneapi-mkl'
diff --git a/doc/source/PreConfiguredSites.rst b/doc/source/PreConfiguredSites.rst
index 094fdd604..32257ea1e 100644
--- a/doc/source/PreConfiguredSites.rst
+++ b/doc/source/PreConfiguredSites.rst
@@ -223,6 +223,14 @@ The following is required for building new spack environments with GNU on this p
    module unload cray-libsci
    module load cray-libsci/23.05.1.4
 
+.. warning::
+   After the successful build of a spack-stack environment, a utility script ``util/narwhal/fix_libsci.sh`` must be run to replace references to an old version of ``libsci`` in several shared libraries. See https://github.com/JCSDA/spack-stack/pull/1449 and https://github.com/JCSDA/spack-stack/issues/1447 for more information.
+
+.. code-block:: console
+
+   # After running 'spack install' (or after 'spack stack setup-meta-modules')
+   ./util/narwhal/fix_libsci.sh 2>&1 | tee log.ENV_NAME_HERE.fix_libsci.001
+
 
 .. _Preconfigured_Sites_Nautilus:
 
diff --git a/util/narwhal/fix_libsci.sh b/util/narwhal/fix_libsci.sh
new file mode 100755
index 000000000..5c96f28ca
--- /dev/null
+++ b/util/narwhal/fix_libsci.sh
@@ -0,0 +1,101 @@
+#!/usr/bin/env bash
+
+# Utility script to work arounds issues on Narwhal, where an old cray-libsci
+# implementation is found and used by spack packages that use autotools,
+# libtool, and configure. This is because of symbolic links in /opt/cray/pe/lib64
+# pointing to the old (v21) libsci installation, and /etc/ld.so.conf.d/ containing
+# a file that tells the build system to include libraries from /opt/cray/pe/lib64.
+
+# The approach is to scan all shared libraries in a spack-stack environment and
+# use patchelf to replace the "bad" libsci references in those with references
+# to the "good" libsci version (determined by looking at the module that is loaded).
+
+# Check input requirements
+echo
+echo "Checking for patchelf ..."
+which patchelf || (echo "ERROR, patchelf not found!" && exit 1)
+
+echo
+echo "Checking for active spack environment ..."
+[ ! -z ${SPACK_ENV} ] && echo ${SPACK_ENV} \
+    || (echo "ERROR, not in an active spack environment!" && exit 1)
+
+echo
+echo "Checking for libsci in user environment ..."
+[ ! -z ${CRAY_LIBSCI_PREFIX} ] && echo ${CRAY_LIBSCI_PREFIX} \
+    || (echo "ERROR, CRAY_LIBSCI_PREFIX not defined!" && exit 1)
+
+BAD_LIBSCI_PATH="/opt/cray/pe/lib64"
+GOOD_LIBSCI_PATH="${CRAY_LIBSCI_PREFIX}/lib"
+LIBSCI_PREFIX="libsci"
+
+echo
+for shlib in `lfs find ${SPACK_ENV}/install -type f -name 'lib*.so*'`; do
+  # Skip backups taken by this program
+  if [[ "${shlib}" == *"backup.libsci-original"* ]]; then
+    echo "Skipping ${shlib} ..."
+    continue
+  fi
+  # Check shared library
+  echo "Checking ${shlib} ..."
+  # First pass: check and fix, second pass: re-check and error out if still bad
+  for (( pass=1; pass<=2; pass++ )); do
+    # Check if grep finds a link to the bad libsci (if so, $? is zero)
+    ldd $shlib | grep ${BAD_LIBSCI_PATH}/${LIBSCI_PREFIX} > /dev/null 2>&1
+    if [[ $? -eq 0 ]]; then
+      if [[ ${pass} -eq 1 ]]; then
+        echo "Fixing ${shlib} ..."
+      elif [[ ${pass} -eq 2 ]]; then
+        echo "ERROR, when re-checking ${shlib}, still found bad libsci links!"
+        ldd $shlib | grep ${BAD_LIBSCI_PATH}/${LIBSCI_PREFIX}
+        exit 1
+      fi
+      # Get all offending references to the "bad" libsci (split multiline string into array)
+      results=`ldd $shlib | grep ${BAD_LIBSCI_PATH}/${LIBSCI_PREFIX}`
+      IFS=$'\n' read -r -d '' -a results <<< "$results"
+      # Loop over lines containing references to "bad" libsci
+      for (( i=0; i<${#results[@]}; i++ )); do
+        # Split each line into items by whitespace
+        IFS=' ' read -r -a items <<< "${results[$i]}"
+        # Remove all leading and trailing whitespaces from each of the items
+        for (( j=0; j<${#items[@]}; j++ )); do
+          items[$j]=$(sed -e 's/^[[:space:]]*//' -e 's/[[:space:]]*$//'<<<"${items[$j]}")
+        done
+        # Sanity check 1. The item with index 1 must be '=>' after removing whitespaces
+        if [[ ! "${items[1]}" == "=>" ]]; then
+          echo "ERROR parsing ldd output for file ${shlib}: '${results[$i]}'"
+          exit 1
+        fi
+        # Sanity check 2. The name of the library (item[0]) must match the
+        # name of the library it is linked to (filename from target path item[2])
+        libname=${items[0]}
+        test_libname=$(echo "${items[2]}" | rev | cut -d'/' -f1 | rev)
+        if [[ ! "${items[0]}" == "${test_libname}" ]]; then
+          echo "ERROR matching library name in ldd output for file ${shlib}: '${results[$i]}'"
+          exit 1
+        fi
+        replacement=${GOOD_LIBSCI_PATH}/${libname}
+        # Sanity check 3. The library must exist in the "good" libsci path.
+        if [[ ! -e ${replacement} ]]; then
+          echo "ERROR, replacement ${replacement} for ${to_replace} does not exist!"
+          exit 1
+        fi
+        # Create a backup of the original shared library and replace the old
+        # library (referenced as ${libname}) with the new one (${replacement})
+        if [[ ! -f ${shlib}.backup.libsci-original ]]; then
+          echo "Creating backup ${shlib}.backup.libsci-original"
+          cp -a ${shlib} ${shlib}.backup.libsci-original
+        fi
+        # Patch shared library. Replace reference (rpath/direct link) with direct link
+        echo "Executing 'patchelf --replace-needed ${libname} ${replacement} ${shlib}'"
+        patchelf --replace-needed ${libname} ${replacement} ${shlib}
+        if [[ $? -ne 0 ]]; then
+          echo "ERROR executing 'patchelf --replace-needed ${libname} ${replacement} ${shlib}'"
+          exit 1
+        fi
+      done
+    else
+      break
+    fi
+  done
+done