This is the 5085th most frequent Russian word.
морем
"Морем" is the instrumental case of "море," meaning "by the sea" or "with the sea."
"Морем" is used as an instrumental case, indicating that the admiration is related to the location or entity of the 'sea'.
Мы восхищались морем с берега.
We admired the sea from the shore.
"Морем" here is metaphorical, describing an abundance of flowers as resembling the vastness of a sea, also in the instrumental case.
Он украсил стол морем цветов.
He decorated the table with a sea of flowers.
"Морем" serves to indicate the means of travel, specified using the instrumental case.