Here's a generalization of a snippet I posted earlier (which, BTW, had a my bug, now fixed); it does both maxima and minima:

use strict;
my $input_file = 'foobar.txt';
open my $in, $input_file or die "Failed to read $input_file: $!\n";

my @max = do { local $_ = <$in>; chomp; [ split ] };
my @min = ( [ @{ $max[ 0 ] } ] );

my $last = $max[ 0 ][ 1 ];

while ( <$in> ) {
  chomp;
  my ( $x, $y ) = split;
  if ( $y > $last ) {
    $max[ -1 ] = [ $x, $y ];
  }
  elsif ( $max[ -1 ] ) {
    $max[ @max ] = undef;
  }
  if ( $y < $last ) {
    $min[ -1 ] = [ $x, $y ];
  }
  elsif ( $min[ -1 ] ) {
    $min[ @min ] = undef;
  }
  $last = $y;
}
close $in;

pop @max unless $max[ -1 ];
pop @min unless $min[ -1 ];

print "Maxima:\n";
print "($_->[ 0 ], $_->[ 1 ])\n" for @max;

print "Minima:\n";
print "($_->[ 0 ], $_->[ 1 ])\n" for @min;
__END__
Maxima:
(4.133, 4580.870000)
(4.160, 4544.999000)
(4.413, 2473.469000)
(4.547, 2663.464000)
(4.773, 2588.583000)
Minima:
(4.147, 4522.753000)
(4.307, 1094.119000)
(4.467, 2029.188000)
(4.680, 814.717000)
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